Polynucleotide encoding luciferase

ABSTRACT

Briefly described, embodiments of this disclosure include polynucleotides that encode mutant Cnidarian luciferases that exhibit modulated properties as compared to the corresponding wild-type luciferases, and the modulated properties include at least one of: modulated stability; enhanced light output; and modulated emission maximum. Embodiments of the present disclosure also include polypeptides or fragments thereof encoded by the polynucleotides, constructs including the polynucleotide, expression cassettes, cells, methods of producing the polynucleotides and polypeptides, antibodies, transgenic cells and/or animals, kits, and the like.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to “LUCIFERASES AND METHODS FOR MAKINGAND USING THE SAME,” having Ser. No. PCT/US2006/034601, filed on Sep. 6,2006. This application claims priority to each of the following U.S.provisional applications: “LUCIFERASES AND METHODS FOR MAKING AND USINGTHE SAME,” having Ser. No. 60/714,640, filed on Sep. 6, 2005; “IMPROVEDLUCIFERASES AND METHODS FOR MAKING AND USING THE SAME,” having Ser. No.60/714,969, filed on Sep. 7, 2005; and “RED-SHIFTED RENILLA LUCIFERASEPROTEINS AND METHODS OF USE THEREOF,” having Ser. No. 60/834,752, filedon Aug. 1, 2006, each of which are entirely incorporated herein byreference.

FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

This invention: was made with Government support under contract CA082214awarded by the National Institutes of Health. The Government has certainrights in this invention.

BACKGROUND

Luminescence is a phenomenon in which energy is specifically channeledto a molecule to produce an excited state. Return to a lower energystate is accompanied by release of a photon. Luminescence includesfluorescence, phosphorescence, chemiluminescence and bioluminescence.Bioluminescence is the process by which living organisms emit light thatis visible to other organisms. Where the luminescence isbioluminescence, creation of the excited state derives from an enzymecatalyzed reaction.

During the past twenty years, high-sensitivity biochemical assays usedin research and in medicine have increasingly employed luminescence andfluorescence rather than radioisotopes. This change has been drivenpartly by the increasing expense of radioisotope disposal and partly bythe need to find more rapid and convenient assay methods. More recently,the need to perform biochemical assays in situ in living cells and wholeanimals has driven researchers toward protein-based luminescence andfluorescence.

Since the cloning of a luciferase from the firefly, luciferase geneshave become essential components of biological research. They are usedubiquitously as reporter genes in cell culture experiments, and theiruse as reporters has been extended into the context of small animalimaging. Recently, it has been proposed that the luciferase proteinitself could be conjugated to other proteins such as antibodies orgrowth factors, and these bioluminescently labeled ligands could then beused for imaging of receptor targets in small animals. The advantage ofusing a bioluminescent entity to label a protein over similarfluorescent or radioactive approaches is that in the context of smallanimal imaging the bioluminescent approach has the potential to be moresensitive.

The beetle luciferases (e.g., firefly), however, are not optimal foremployment as bioluminescent tags. These luciferases are notparticularly small (˜62 kDa) and are dependent on ATP, molecular oxygen,and magnesium for activity. The dependence on ATP especially wouldhinder the application of beetle luciferases as bioluminescent tags invivo, since serum ATP concentrations are generally below 10 nM.

Luciferases that use coelenterazine as their substrate are moreappropriate for application as bioluminescent tags, as these enzymes arenot ATP dependent and in general require only molecular oxygen inaddition to coelenterazine for luminescence. From this group ofproteins, the luciferase from Renilla reniformis (RLuc1) is the bestcharacterized, in addition to being of a size (36 kDa) more appropriatefor use as a tag.

The limiting factor for use of RLuc as a bioluminescent tag is itslimited stability under in vivo conditions. A single point mutation ofRLuc (C124A) that increases the enzyme's stability several fold has beenreported, however even this level of stability is insufficient for thetagging of large proteins (e.g., antibodies) that require time scales onthe order of days to sufficiently distribute.

An additional limitation to the use of any of the known coelenterazineutilizing luciferases is that the spectral peaks of these luciferaseslie in the blue region of the visible spectrum. For in vitro assays suchas cell culture transfection studies, the wavelength of light that aluciferase yields is usually of little consequence. For in vivo assayssuch as small animal imaging studies, the wavelength is importantbecause biological tissues are less attenuating to the red andnear-infrared portions of the optical spectrum. In the case of RenillaLuciferase the spectral peak is at 482 nm, with only about 3-4% of thephotons of wavelengths above 600 nm. For luciferase at depths greaterthan superficial depths, the majority of the photons that actually makeit out of the animal are these few above 600 nm wavelength photons.

As such, there is a continued need in the art for the development ofluciferases that exhibit improved properties. The present disclosureaddresses this and other needs.

SUMMARY

Briefly described, embodiments of this disclosure includepolynucleotides that encode mutant Cnidarian luciferases that exhibitmodulated properties as compared to the corresponding wild-typeluciferase, and the modulated properties include at least one of:modulated stability; enhanced light output; and modulated emissionmaximum. Embodiments of the present disclosure also include polypeptidesor fragments thereof encoded by the polynucleotides, constructsincluding the polynucleotide, expression cassettes, cells, methods ofproducing the polynucleotides and polypeptides, antibodies, transgeniccells and/or animals, kits, and the like.

An embodiment of the present disclosure includes polynucleotides thatare present in other than their naturally occurring environment and thatencode a mutant Cnidarian luciferase. The mutant Cnidarian luciferaseexhibits modulated properties as compared to its corresponding wild-typeluciferase, and the modulated properties included at least one of:modulated stability, enhanced light output, and modulated emissionmaximum.

An embodiment of the present disclosure includes constructs that includea vector and a polynucleotide as described herein.

An embodiment of the present disclosure includes expression cassettesthat include a transcriptional initiation region functional in anexpression host; a polynucleotide as described herein; and atranscriptional termination region functional in the expression host.

An embodiment of the present disclosure includes cells, or the progenythereof, that include an expression cassette as described herein as partof an extrachromosomal element or integrated into the genome of a hostcell as a result of introduction of the expression cassette into thehost cell.

An embodiment of the present disclosure includes methods of producing aluciferase that include growing a cell as described herein, whereby theprotein is expressed, and isolating the protein so that it issubstantially free of other proteins.

An embodiment of the present disclosure includes proteins or fragmentsthereof encoded by a polynucleotide as described herein.

An embodiment of the present disclosure includes antibodies bindingspecifically to a protein as described herein.

An embodiment of the present disclosure includes transgenic cells or theprogeny thereof that include a transgene that includes a polynucleotideas described herein.

An embodiment of the present disclosure includes transgenic organismsthat include a transgene that includes a polynucleotide as describedherein.

An embodiment of the present disclosure includes applications asdescribed herein that employ the polynucleotides and/or polypeptides orfragments thereof as described herein.

An embodiment of the present disclosure includes kits that include apolynucleotide as described herein.

An embodiment of the present disclosure includes kits that include aprotein or fragment thereof encoded by a polynucleotide as describedherein.

An embodiment of the present disclosure includes polynucleotides thatencode a mutant Cnidarian luciferase. The mutant Cnidarian luciferaseexhibits modulated properties as compared to its corresponding wild-typeluciferase, and the modulated properties include at least one of:modulated stability, enhanced light output, and modulated emissionmaximum.

An embodiment of the present disclosure includes polypeptides havingmodulated properties as compared to their corresponding wild-typeluciferase and where the modulated properties include at least one of:modulated stability, enhanced light output, and modulated emissionmaximum.

BRIEF DESCRIPTION OF THE FIGURES

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 illustrates the chemical structures of coelenterazine and severalanalogs.

FIG. 2 illustrates a coomassie stained SDS-PAGE gel of RLuc and RLuc8 atseveral points during the purification process. The lanes are labeled asfollows: M—Marker, P—Periplasmic fraction, FT—Flow through from nickelaffinity column, W—Wash from column, E—Elution from column. As theelution volume is 5% of the periplasmic fraction, the periplasmicfraction, flow through, and wash were concentrated twenty fold using 3kDa cut-off centrifugal concentrators (Pall, Ann Arbor, Mich.). Theexpected sizes for RLuc and RLuc8 are 38.7 kDa and 36.9 kDa,respectively, with the difference in size arising from a Myc epitopeadded by the expression vector used for RLuc. These protein masses wereconfirmed by MALDI-TOF. Final recovery of purified protein was typically5 mg/L of culture for RLuc, and 50 mg/L of culture for RLuc8.

FIG. 3A illustrates mouse serum stability data for RLuc, RLuc8, andseveral other mutations. The polypeptides were incubated in mouse serumat 37° C. in triplicate, with aliquots removed at various times todetermine the remaining luciferase activity. The error bars representthe standard error of the mean, and the lines drawn between the pointsare from mono-exponential curve fits. FIG. 3B illustrates a normalizedbioluminescence emission spectra for RLuc, RLuc8, and several othermutations. The normalized emission spectrum of RLuc8 when used withbisdeoxycoelenterazine (bdc) is also included for comparison.

FIG. 4A illustrates a homology model of Renilla luciferase based on itssimilarity to the haloalkane de-halogenase LinB. The region of theenzyme from residue 35 to 309 was successfully modelled usingSwiss-Model and is shown. The N-terminus is blue and the C-terminus isred. The presumptive active site is located at the intersection of thered, green, and green-cyan loops. FIG. 4B illustrates a close up of thehomology model showing the potential active site. The side chains forthe potential active site residues D120, E144, and H285 are shown, alongwith the mutation site M185.

FIG. 5 Illustrates different ionic forms of coelenteramide havedifferent fluorescent emission peaks. The bioluminescent emissionspectrum of the Renilla luciferase catalyzed oxidation of coelenterazineis believed to be related to the fluorescent emission spectrum of theproduct of that reaction, coelenteramide.

FIG. 6 illustrates that mutations in Renilla luciferase's substratebinding pocket (or enzymatic pocket) can lead to shifts in thebioluminescent emission spectrum.

FIG. 7 illustrates mammalian cell expression of native RLuc and severalmutants following transient transfection into 293T cells. Light outputper total cellular protein was recorded for each condition, and isreported as relative to the value of the RLuc condition at the giventime point.

FIG. 8 illustrates the intracellular inactivation of luciferase activityfor several of the luciferase variants. The estimated intracellularactivity half-lives are given in the figure key.

FIG. 9A illustrates a schematic diagram of RL8-VEGF fusion reporterprotein binding to target receptors on cells. The novel probe can targetreceptors (VEGFR-2/FLT-1) based on the targeting moiety (e.g., VEGF121dimer). The enzymatic reporter moiety (RL8) can then oxidize itssubstrate coelenterazine into coelenteramide without the need for ATP,leading to detectable photon emission. FIG. 9B illustrates an assemblyof genes encoding novel fusion reporter probe RL8-VEGF. A directionalcloning strategy was used to ligate the human VEGF 121 cDNA in-frame tothe Rluc8 mutant gene resulting in a leu-gly (LG) linker. Ahexahistidine sequence in the C-terminal protein was used for nickelcolumn purification of the protein from the periplasmic fraction of LMG194 Escherichia coli.

FIG. 10A illustrates coomassie Blue staining of purified fusion proteinsand control proteins. Lane 1: RL8-VEGF, Lane 2: RL8-RIK 83.2 bindingmutant, Lane 3: Rluc8 only. The 50 kDa fusion proteins are thepredominant bands in Lane 1 and Lane 2 for RL8-VEGF and RL8-RIK 83.2,respectively. The Rluc8 lane shows a dominant 36 kDa band as expectedand a possible dimerization band in Lane 3. FIG. 10B illustrates aWestern Blot of purified proteins. The first panel shows anti-C-terminalhistidine tag antibody detection of the purified proteins. Afterstripping of the membrane, an anti-Renilla luciferase antibody was usedto re-probe and showed the identification of the same bands recognizedby the anti-C-terminal histidine tag antibody. FIG. 10C illustratescompetitive bioluminescence ELISA on PAE/VEGFR-2 overexpressing cells.RL8-VEGF fusion protein preferentially bound to VEGFR-2 over-expressingcells (PAE/VEGFR-2), while the RIK83.2 binding mutant showed 80% loss ofbinding. Increasing the “cold” VEGF 121 concentration (in ng/mL) showeda dose-dependent competition for VEGFR-2 binding with RL8-VEGF. Fiftypercent inhibition of binding of RL8-VEGF was achieved at 45 ng/mL VEGF121. The RIK 83.2 binding mutant showed no effect from competition byVEGF 121.

FIG. 11A illustrates an in vitro assay for serum stability. Onemicrogram of indicated RL8-VEGF fusion reporter probe or Rluc8 controlprotein was incubated at 37° C. in 50 microliters of mouse serum at 0,2, 4, 8, 12, 24, and 48 hours. Aliquots were incubated withcoelenterazine substrate and assayed for luciferase activity in aluminometer. Values are represented as percent of Time 0 hoursluciferase activity. FIG. 11B illustrates the serum effect onbifunctional reporter protein affinity. The RL8-VEGF and RL8-RIK 83.2binding mutant fusion proteins were incubated at 37° C. at the indicatedtimes. The cell binding affinities using bioluminescence ELISA wastested on PAE/VEGFR-2 cells and showed 75% retention of binding up to 48hours of incubation. The RL8-RIK 83.2 binding mutant showed asignificant loss of binding compared with the RL8-VEGF fusion proteinafter 48 hours of serum incubation.

FIG. 12 illustrates an estimation for the coelenterazine orientation inthe context of a Swiss-Model derived RLuc8 homology model. The schematicshows which residues putatively interact with the substrate based on theestimate.

FIG. 13 illustrates normalized bioluminescence emission spectra for twoof the red-shifted variants of RLuc8 that were developed. The spectrawere applied after applying coelenterazine to the purified proteins. Thenormalization equalized the total area under the curve. The spectra forthe click beetle luciferases are from Zhao et al, Mol. Imaging. 3:43-54,2004 (which is incorporated by reference), and are included forcomparison.

DETAILED DESCRIPTION

Before the present disclosure is described in greater detail, it is tobe understood that this disclosure is not limited to particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting, since the scope of the present disclosure will be limited onlyby the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the disclosure. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the disclosure, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the disclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present disclosure, the preferredmethods and materials are now described.

All publications and patents cited in this specification are hereinincorporated by reference as if each individual publication or patentwere specifically and individually indicated to be incorporated byreference and are incorporated herein by reference to disclose anddescribe the methods and/or materials in connection with which thepublications are cited. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that the present disclosure is not entitled to antedate suchpublication by virtue of prior disclosure. Further, the dates ofpublication provided could be different from the actual publicationdates that may need to be independently confirmed.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentdisclosure. Any recited method can be carried out in the order of eventsrecited or in any other order that is logically possible.

Embodiments of the present disclosure will employ, unless otherwiseindicated, techniques of synthetic organic chemistry, biochemistry,biology, molecular biology, and the like, which are within the skill ofthe art. Such techniques are explained fully in the literature.

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how toperform the methods and use the compositions and compounds disclosed andclaimed herein. Efforts have been made to ensure accuracy with respectto numbers (e.g., amounts, temperature, etc.), but some errors anddeviations should be accounted for. Unless indicated otherwise, partsare parts by weight, temperature is in ° C., and pressure is at or nearatmospheric. Standard temperature and pressure are defined as 20° C. and1 atmosphere.

Before the embodiments of the present disclosure are described indetail, it is to be understood that, unless otherwise indicated, thepresent disclosure is not limited to particular materials, reagents,reaction materials, manufacturing processes, or the like, as such canvary. It is also to be understood that the terminology used herein isfor purposes of describing particular embodiments only, and is notintended to be limiting. It is also possible in the present disclosurethat steps can be executed in different sequence where this is logicallypossible.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a support” includes a plurality of supports. In thisspecification and in the claims that follow, reference will be made to anumber of terms that shall be defined to have the following meaningsunless a contrary intention is apparent.

DEFINITIONS

In describing and claiming the disclosed subject matter, the followingterminology will be used in accordance with the definitions set forthbelow.

In accordance with the present disclosure there may be employedconventional molecular biology, microbiology, and recombinant DNAtechniques within the skill of the art. Such techniques are explainedfully in the literature. See, e.g., Maniatis, Fritsch & Sambrook,“Molecular Cloning: A Laboratory Manual (1982); “DNA Cloning: APractical Approach,” Volumes I and II (D. N. Glover ed. 1985);“Oligonucleotide Synthesis” (M. J. Gait ed. 1984); “Nucleic AcidHybridization” (B. D. Hames & S. J. Higgins eds. (1985)); “Transcriptionand Translation” (B. D. Hames & S. J. Higgins eds. (1984)); “Animal CellCulture” (R. I. Freshney, ed. (1986)); “Immobilized Cells and Enzymes”(IRL Press, (1986)); B. Perbal, “A Practical Guide To Molecular Cloning”(1984), each of which is incorporated herein by reference.

“Bioluminescent donor protein” refers to a protein capable of acting ona bioluminescent initiator molecule to generate bioluminescence.

“Bioluminescent initiator molecule” is a molecule that can react with abioluminescent donor protein to generate bioluminescence.

As used herein, the terms “antibody” and “antibodies” can include, butare not limited to, monoclonal antibodies, multispecific antibodies,human antibodies, humanized antibodies, camelised antibodies, chimericantibodies, single-chain Fvs (scFv), single chain antibodies, Fabfragments, F(ab′) fragments, disulfide-linked Fvs (sdFv), andanti-idiotypic (anti-Id) antibodies (e.g., anti-Id antibodies toantibodies of the disclosure), and epitope-binding fragments of any ofthe above. In particular, antibodies include immunoglobulin moleculesand immunologically active fragments of immunoglobulin molecules (e.g.,molecules that contain an antigen binding site). Immunoglobulinmolecules can be of any type (e.g., IgG, IgE, IgM, IgD, IgA and IgY),class (e.g., IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2), or subclass. Theantibodies may be from any animal origin including birds and mammals(e.g., human, murine, donkey, sheep, rabbit, goat, guinea pig, camel,horse, or chicken). Preferably, the antibodies are human or humanizedmonoclonal antibodies. As used herein, “human” antibodies includeantibodies having the amino acid sequence of a human immunoglobulin andinclude antibodies isolated from human immunoglobulin libraries or frommice that express antibodies from human genes. The antibodies may bemonospecific, bispecific, trispecific, or of greater multispecificity.

As used herein, “humanized” describes antibodies wherein some, most orall of the amino acids outside the CDR regions are replaced withcorresponding amino acids derived from human immunoglobulin molecules.In one embodiment of the humanized forms of the antibodies, some, most,or all of the amino acids outside the CDR regions have been replacedwith amino acids from human immunoglobulin molecules but where some,most, or all amino acids within one or more CDR regions are unchanged.Small additions, deletions, insertions, substitutions or modificationsof amino acids are permissible as long as they would not abrogate theability of the antibody to bind a given antigen. Suitable humanimmunoglobulin molecules would include IgG1, IgG2, IgG3, IgG4, IgA andIgM molecules. A “humanized” antibody would retain a similar antigenicspecificity as the original antibody.

Bioluminescence (BL) is defined as emission of light by living organismsthat is well visible in the dark and affects visual behavior of animals(See e.g., Harvey, E. N. (1952). Bioluminescence. New York: AcademicPress; Hastings, J. W. (1995). Bioluminescence. In: Cell Physiology (ed.by N. Speralakis). pp. 651-681. New York: Academic Press. Wilson, T. andHastings, J. W. (1998). Bioluminescence. Annu Rev Cell Dev Biol 14,197-230.). Bioluminescence does not include so-called ultra-weak lightemission, which can be detected in virtually all living structures usingsensitive luminometric equipment (Murphy, M. E. and Sies, H. (1990),Meth. Enzymol 186, 595-610; Radotic, K, Radenovic, C, Jeremic, M.(1998), Gen Physiol Biophys 17, 289-308). Bioluminescence also does notinclude weak light emissions, which most probably does not play anyecological role, such as the glowing of bamboo growth cone (Totsune, H.,Nakano, M., Inaba, H. (1993), Biochem. Biophys. Res Comm. 194,1025-1029). Bioluminescence also does not include emission of lightduring fertilization of animal eggs (Klebanoff, S. J., Froeder, C. A.,Eddy, E. M., Shapiro, B. M. (1979), J. Exp. Med. 149, 938-953; Schomer,B. and Epel, D. (1998), Dev Biol 203, 1-11).

The term “polymer” means any compound that is made up of two or moremonomeric units covalently bonded to each other, where the monomericunits may be the same or different, such that the polymer may be ahomopolymer or a heteropolymer. Representative polymers includepeptides, polysaccharides, nucleic acids and the like, where thepolymers may be naturally occurring or synthetic.

The term “polypeptides” includes proteins and fragments thereof.Polypeptides are disclosed herein as amino acid residue sequences. Thosesequences are written left to right in the direction from the amino tothe carboxy terminus. In accordance with standard nomenclature, aminoacid residue sequences are denominated by either a three letter or asingle letter code as indicated as follows: Alanine (Ala, A), Arginine(Arg, R), Asparagine (Asn, N), Aspartic Acid (Asp, D), Cysteine (Cys,C), Glutamine (Gln, Q), Glutamic Acid (Glu, E), Glycine (Gly, G),Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys,K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P),Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr,Y), and Valine (Val, V).

“Variant” refers to a polypeptide or polynucleotide that differs from areference polypeptide or polynucleotide, but retains essentialproperties. A typical variant of a polypeptide differs in amino acidsequence from another, reference polypeptide. Generally, differences arelimited so that the sequences of the reference polypeptide and thevariant are closely similar overall and, in many regions, identical. Avariant and reference polypeptide may differ in amino acid sequence byone or more modifications (e.g., substitutions, additions, and/ordeletions). A variant of a polypeptide includes conservatively modifiedvariants. A substituted or inserted amino acid residue may or may not beone encoded by the genetic code. A variant of a polypeptide may benaturally occurring, such as an allelic variant, or it may be a variantthat is not known to occur naturally.

Modifications and changes can be made in the structure of thepolypeptides of this disclosure and still obtain a molecule havingsimilar characteristics as the polypeptide (e.g., a conservative aminoacid substitution). For example, certain amino acids can be substitutedfor other amino acids in a sequence without appreciable loss ofactivity. Because it is the interactive capacity and nature of apolypeptide that defines that polypeptide's biological functionalactivity, certain amino acid sequence substitutions can be made in apolypeptide sequence and nevertheless obtain a polypeptide with likeproperties.

In making such changes, the hydropathic index of amino acids can beconsidered. The importance of the hydropathic amino acid index inconferring interactive biologic function on a polypeptide is generallyunderstood in the art. It is known that certain amino acids can besubstituted for other amino acids having a similar hydropathic index orscore and still result in a polypeptide with similar biologicalactivity. Each amino acid has been assigned a hydropathic index on thebasis of its hydrophobicity and charge characteristics. Those indicesare: isoleucine (+4.5); valine (+4.2); leucine (+3.8); phenylalanine(+2.8); cysteine/cysteine (+2.5); methionine (+1.9); alanine (+1.8);glycine (−0.4); threonine (−0.7); serine (−0.8); tryptophan (−0.9);tyrosine (−1.3); proline (−1.6); histidine (−3.2); glutamate (−3.5);glutamine (−3.5); aspartate (−3.5); asparagine (−3.5); lysine (−3.9);and arginine (−4.5).

It is believed that the relative hydropathic character of the amino aciddetermines the secondary structure of the resultant polypeptide, whichin turn defines the interaction of the polypeptide with other molecules,such as enzymes, substrates, receptors, antibodies, antigens, and thelike. It is known in the art that an amino acid can be substituted byanother amino acid having a similar hydropathic index and still obtain afunctionally equivalent polypeptide. In such changes, the substitutionof amino acids whose hydropathic indices are within ±2 is preferred,those within ±1 are particularly preferred, and those within ±0.5 areeven more particularly preferred.

Substitution of like amino acids can also be made on the basis ofhydrophilicity, particularly, where the biological functional equivalentpolypeptide or peptide thereby created is intended for use inimmunological embodiments. The following hydrophilicity values have beenassigned to amino acid residues: arginine (+3.0); lysine (+3.0);aspartate (+3.0±1); glutamate (+3.0±1); serine (+0.3); asparagine(+0.2); glutamine (+0.2); glycine (0); proline (−0.5±1); threonine(−0.4); alanine (−0.5); histidine (−0.5); cysteine (−1.0); methionine(−1.3); valine (−1.5); leucine (−1.8); isoleucine (−1.8); tyrosine(−2.3); phenylalanine (−2.5); tryptophan (−3.4). It is understood thatan amino acid can be substituted for another having a similarhydrophilicity value and still obtain a biologically equivalent, and inparticular, an immunologically equivalent polypeptide. In such changes,the substitution of amino acids whose hydrophilicity values are within±2 is preferred, those within ±1 are particularly preferred, and thosewithin ±0.5 are even more particularly preferred.

As outlined above, amino acid substitutions are generally based on therelative similarity of the amino acid side-chain substituents, forexample, their hydrophobicity, hydrophilicity, charge, size, and thelike. Exemplary substitutions that take various of the foregoingcharacteristics into consideration are well known to those of skill inthe art and include (original residue: exemplary substitution): (Ala:Gly, Ser), (Arg: Lys), (Asn: Gln, His), (Asp: Glu, Cys, Ser), (Gin:Asn), (Glu: Asp), (Gly: Ala), (His: Asn, Gln), (Ile: Leu, Val), (Leu:Ile, Val), (Lys: Arg), (Met: Leu, Tyr), (Ser: Thr), (Thr: Ser), (Tip:Tyr), (Tyr: Trp, Phe), and (Val: Ile, Leu). Embodiments of thisdisclosure thus contemplate functional or biological equivalents of apolypeptide as set forth above. In particular, embodiments of thepolypeptides can include variants having about 50%, 60%, 70%, 80%, 90%,and 95% sequence identity to the polypeptide of interest.

“Identity,” as known in the art, is a relationship between two or morepolypeptide sequences, as determined by comparing the sequences. In theart, “identity” also means the degree of sequence relatedness betweenpolypeptides as determined by the match between strings of suchsequences. “Identity” and “similarity” can be readily calculated byknown methods, including, but not limited to, those described in(Computational Molecular Biology, Lesk, A. M., Ed., Oxford UniversityPress, New York, 1988; Biocomputing: Informatics and Genome Projects,Smith, D. W., Ed., Academic Press, New York, 1993; Computer Analysis ofSequence Data, Part I, Griffin, A. M., and Griffin, H. G., Eds., HumanaPress, New Jersey, 1994; Sequence Analysis in Molecular Biology, vonHeinje, G., Academic Press, 1987; and Sequence Analysis Primer,Gribskov, M. and Devereux, J., Eds., M Stockton Press, New York, 1991;and Carillo, H., and Lipman, D., SIAM J Applied Math., 48: 1073 (1988).

Preferred methods to determine identity are designed to give the largestmatch between the sequences tested. Methods to determine identity andsimilarity are codified in publicly available computer programs. Thepercent identity between two sequences can be determined by usinganalysis software (e.g., Sequence Analysis Software Package of theGenetics Computer Group, Madison Wis.) that incorporates the Needelmanand Wunsch, (J. Mol. Biol., 48: 443-453, 1970) algorithm (e.g., NBLAST,and XBLAST). The default parameters are used to determine the identityfor the polypeptides of the present disclosure.

By way of example, a polypeptide sequence may be identical to thereference sequence, that is 100% identical, or it may include up to acertain integer number of amino acid alterations as compared to thereference sequence such that the % identity is less than 100%. Suchalterations are selected from: at least one amino acid deletion,substitution, including conservative and non-conservative substitution,or insertion, and wherein said alterations may occur at the amino- orcarboxy-terminal positions of the reference polypeptide sequence oranywhere between those terminal positions, interspersed eitherindividually among the amino acids in the reference sequence or in oneor more contiguous groups within the reference sequence. The number ofamino acid alterations for a given % identity is determined bymultiplying the total number of amino acids in the reference polypeptideby the numerical percent of the respective percent identity (divided by100) and then subtracting that product from said total number of aminoacids in the reference polypeptide.

Conservative amino acid variants can also comprise non-naturallyoccurring amino acid residues. Non-naturally occurring amino acidsinclude, without limitation, trans-3-methylproline, 2,4-methanoproline,cis-4-hydroxyproline, trans-4-hydroxyproline, N-methyl-glycine,allo-threonine, methylthreonine, hydroxy-ethylcysteine,hydroxyethylhomocysteine, nitro-glutamine, homoglutamine, pipecolicacid, thiazolidine carboxylic acid, dehydroproline, 3- and4-methylproline, 3,3-dimethylproline, tert-leucine, norvaline,2-azaphenyl-alanine, 3-azaphenylalanine, 4-azaphenylalanine, and4-fluorophenylalanine. Several methods are known in the art forincorporating non-naturally occurring amino acid residues into proteins.For example, an in vitro system can be employed wherein nonsensemutations are suppressed using chemically aminoacylated suppressortRNAs. Methods for synthesizing amino acids and aminoacylating tRNA areknown in the art. Transcription and translation of plasmids containingnonsense mutations is carried out in a cell-free system comprising an E.coli S30 extract and commercially available enzymes and other reagents.Proteins are purified by chromatography. (Robertson, et al., J. Am.Chem. Soc., 113: 2722, 1991; Ellman, et al., Methods Enzymol., 202: 301,1991; Chung, et al., Science, 259: 806-9, 1993; and Chung, et al., Proc.Natl. Acad. Sci. USA, 90: 10145-9, 1993). In a second method,translation is carried out in Xenopus oocytes by microinjection ofmutated mRNA and chemically aminoacylated suppressor tRNAs (Turcatti, etal., J. Biol. Chem., 271: 19991-8, 1996). Within a third method, E. colicells are cultured in the absence of a natural amino acid that is to bereplaced (e.g., phenylalanine) and in the presence of the desirednon-naturally occurring amino acid(s) (e.g., 2-azaphenylalanine,3-azaphenylalanine, 4-azaphenylalanine, or 4-fluorophenylalanine). Thenon-naturally occurring amino acid is incorporated into the protein inplace of its natural counterpart. (Koide, et al., Biochem., 33: 7470-6,1994). Naturally occurring amino acid residues can be converted tonon-naturally occurring species by in vitro chemical modification.Chemical modification can be combined with site-directed mutagenesis tofurther expand the range of substitutions (Wynn, et al., Protein Sci.,2: 395-403, 1993).

As used herein, the term “polynucleotide” generally refers to anypolyribonucleotide or polydeoxyribonucleotide, which may be unmodifiedRNA or DNA or modified RNA or DNA. Thus, for instance, polynucleotidesas used herein refers to, among others, single- and double-stranded DNA,DNA that is a mixture of single- and double-stranded regions, single-and double-stranded RNA, and RNA that is mixture of single- anddouble-stranded regions, hybrid molecules comprising DNA and RNA thatmay be single-stranded or, more typically, double-stranded or a mixtureof single- and double-stranded regions. Polynucleotide encompasses theterms “nucleic acid,” “nucleic acid sequence,” or “oligonucleotide” asdefined above.

In addition, polynucleotide as used herein refers to triple-strandedregions comprising RNA or DNA or both RNA and DNA. The strands in suchregions may be from the same molecule or from different molecules. Theregions may include all of one or more of the molecules, but moretypically involve only a region of some of the molecules. One of themolecules of a triple-helical region often is an oligonucleotide.

As used herein, the term polynucleotide includes DNAs or RNAs asdescribed above that contain one or more modified bases. Thus, DNAs orRNAs with backbones modified for stability or for other reasons are“polynucleotides” as that term is intended herein. Moreover, DNAs orRNAs comprising unusual bases, such as inosine, or modified bases, suchas tritylated bases, to name just two examples, are polynucleotides asthe term is used herein.

It will be appreciated that a great variety of modifications have beenmade to DNA and RNA that serve many useful purposes known to those ofskill in the art. The term polynucleotide as it is employed hereinembraces such chemically, enzymatically or metabolically modified formsof polynucleotides, as well as the chemical forms of DNA and RNAcharacteristic of viruses and cells, including simple and complex cells,inter alias.

By way of example, a polynucleotide sequence of the present disclosuremay be identical to the reference sequence, that is be 100% identical,or it may include up to a certain integer number of nucleotidealterations as compared to the reference sequence. Such alterations areselected from the group including at least one nucleotide deletion,substitution, including transition and transversion, or insertion, andwherein said alterations may occur at the 5′ or 3′ terminal positions ofthe reference nucleotide sequence or anywhere between those terminalpositions, interspersed either individually among the nucleotides in thereference sequence or in one or more contiguous groups within thereference sequence. The number of nucleotide alterations is determinedby multiplying the total number of nucleotides in the referencenucleotide by the numerical percent of the respective percent identity(divided by 100) and subtracting that product from said total number ofnucleotides in the reference nucleotide. Alterations of a polynucleotidesequence encoding the polypeptide may alter the polypeptide encoded bythe polynucleotide following such alterations.

The term “codon” means a specific triplet of mononucleotides in the DNAchain. Codons correspond to specific amino acids (as defined by thetransfer RNAs) or to start and stop of translation by the ribosome.

The term “degenerate nucleotide sequence” denotes a sequence ofnucleotides that includes one or more degenerate codons (as compared toa reference polynucleotide molecule that encodes a polypeptide).Degenerate codons contain different triplets of nucleotides, but encodethe same amino acid residue (e.g., GAU and GAC triplets each encodeAsp).

A DNA “coding sequence” is a DNA sequence that is transcribed andtranslated into a polypeptide in vivo when placed under the control ofappropriate regulatory sequences. The boundaries of the coding sequenceare determined by a start codon at the 5′ (amino) terminus and atranslation stop codon at the 3′ (carboxyl) terminus. A coding sequencecan include, but is not limited to, prokaryotic sequences, cDNA fromeukaryotic mRNA, genomic DNA sequences from eukaryotic (e.g., mammalian)DNA, and synthetic DNA sequences. A polyadenylation signal andtranscription termination sequence may be located 3′ to the codingsequence.

“Operably linked” refers to a juxtaposition wherein the components areconfigured so as to perform their usual function. For example, controlsequences or promoters operably linked to a coding sequence are capableof effecting the expression of the coding sequence, and an organellelocalization sequence operably linked to protein will direct the linkedprotein to be localized at the specific organelle.

As used herein, the term “exogenous DNA” or “exogenous nucleic acidsequence” or “exogenous polynucleotide” refers to a nucleic acidsequence that was introduced into a cell or organelle from an externalsource. Typically the introduced exogenous sequence is a recombinantsequence.

A cell has been “transformed” or “transfected” by a nucleic acidsequence such as an exogenous or a heterologous DNA when such DNA hasbeen introduced inside the cell. The transforming DNA may or may not beintegrated (covalently linked) into the genome of the cell. Inprokaryotes, yeast, and mammalian cells for example, the transformingDNA may be maintained on an episomal element such as a plasmid. Withrespect to eukaryotic cells, a stably transformed cell is one in whichthe transforming DNA has become integrated into a chromosome so that itis inherited by daughter cells through chromosome replication. Thisstability is demonstrated by the ability of the eukaryotic cell toestablish cell lines or clones comprised of a population of daughtercells containing the transforming DNA. A “clone” is a population ofcells derived from a single cell or common ancestor by mitosis. A “cellline” is a clone of a primary cell that is capable of stable growth invitro for many generations. The nucleic acid may be in the form of nakedDNA or RNA, associated with various proteins or the nucleic acid may beincorporated into a vector.

A “heterologous” region of a DNA construct is an identifiable segment ofDNA within a larger DNA molecule that is not found in association withthe larger molecule in nature. Thus, when the heterologous regionencodes a mammalian gene, the gene will usually be flanked by DNA thatdoes not flank the mammalian genomic DNA in the genome of the sourceorganism. In another example, heterologous DNA includes coding sequencein a construct where portions of genes from two different sources havebeen brought together so as to produce a fusion protein product. Allelicvariations or naturally-occurring mutational events do not give rise toa heterologous region of DNA as defined herein.

As used herein, the term “vector” or “expression vector” is used todenote a DNA molecule, linear or circular, which includes a segmentencoding a polypeptide of interest operably linked to additionalsegments that provide for its transcription and translation uponintroduction into a host cell or host cell organelles. Such additionalsegments include promoter and terminator sequences, and may also includeone or more origins of replication, one or more selectable markers, anenhancer, a polyadenylation signal, etc. Expression vectors aregenerally derived from yeast or bacterial genomic or plasmid DNA, orviral DNA, or may contain elements of one or more of the above.

“DNA regulatory sequences”, as used herein, are transcriptional andtranslational control sequences, such as promoters, enhancers,polyadenylation signals, terminators, and the like, that provide forand/or regulate expression of a coding sequence in a host cell.

A “promoter sequence” is a DNA regulatory region capable of binding RNApolymerase in a cell and initiating transcription of a downstream (3′direction) coding sequence. For purposes of defining the presentdisclosure, the promoter sequence is bounded at its 3′ terminus by thetranscription initiation site and extends upstream (5′ direction) toinclude the minimum number of bases or elements necessary to initiatetranscription at levels detectable above background. Within the promotersequence will be found a transcription initiation site, as well asprotein binding domains responsible for the binding of RNA polymerase.Eukaryotic promoters will often, but not always, contain “TATA” boxesand “CAT” boxes. Various promoters, including inducible promoters, maybe used to drive the various vectors of the present disclosure.

As used herein, the terms “restriction endonucleases” and “restrictionenzymes” refer to bacterial enzymes, each of which cut double-strandedDNA at or near a specific nucleotide sequence.

A cell has been “transformed” or “transfected” by exogenous orheterologous DNA when such DNA has been introduced inside the cell. Thetransforming DNA may or may not be integrated (covalently linked) intothe genome of the cell. In prokaryotes, yeast, and mammalian cells forexample, the transforming DNA may be maintained on an episomal elementsuch as a plasmid. With respect to eukaryotic cells, a stablytransformed cell is one in which the transforming DNA has becomeintegrated into a chromosome so that it is inherited by daughter cellsthrough chromosome replication. This stability is demonstrated by theability of the eukaryotic cell to establish cell lines or clonescomprised of a population of daughter cells containing the transformingDNA. A “clone” is a population of cells derived from a single cell orcommon ancestor by mitosis. A “cell line” is a clone of a primary cellthat is capable of stable growth in vitro for many generations.

As used herein, the term “reporter gene” refers to a coding sequenceattached to heterologous promoter or enhancer elements and whose productmay be assayed easily and quantifiably when the construct is introducedinto tissues or cells.

As used herein, the term “hybridization” refers to the process ofassociation of two nucleic acid strands to form an antiparallel duplexstabilized by means of hydrogen bonding between residues of the oppositenucleic acid strands.

The term “immunologically active” defines the capability of the natural,recombinant or synthetic bioluminescent protein, or any oligopeptidethereof, to induce a specific immune response in appropriate animals orcells and to bind with specific antibodies. As used herein, “antigenicamino acid sequence” means an amino acid sequence that, either alone orin association with a carrier molecule, can elicit an antibody responsein a mammal. The term “specific binding,” in the context of antibodybinding to an antigen, is a term well understood in the art and refersto binding of an antibody to the antigen to which the antibody wasraised, but not other, unrelated antigens.

As used herein the term “isolated” is meant to describe apolynucleotide, a polypeptide, an antibody, or a host cell that is in anenvironment different from that in which the polynucleotide, thepolypeptide, the antibody, or the host cell naturally occurs.

“Optional” or “optionally” means that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.

“Hybridizing” and “binding”, with respect to polynucleotides, are usedinterchangeably. The terms “hybridizing specifically to” and “specifichybridization” and “selectively hybridize to,” as used herein refer tothe binding, duplexing, or hybridizing of a nucleic acid moleculepreferentially to a particular nucleotide sequence under stringentconditions.

The term “stringent assay conditions” as used herein refers toconditions that are compatible to produce binding pairs of nucleic acids(e.g., surface bound and solution phase nucleic acids) of sufficientcomplementarity to provide for the desired level of specificity in theassay while being less compatible to the formation of binding pairsbetween binding members of insufficient complementarity to provide forthe desired specificity. Stringent assay conditions are the summation orcombination (totality) of both hybridization and wash conditions.

“Stringent hybridization conditions” and “stringent hybridization washconditions” in the context of nucleic acid hybridization (e.g., as inarray, Southern or Northern hybridizations) are sequence dependent, andare different under different experimental parameters. Stringenthybridization conditions that can be used to identify nucleic acidswithin the scope of the disclosure can include, e.g., hybridization in abuffer comprising 50% formamide, 5×SSC, and 1% SDS at 42° C., orhybridization in a buffer comprising 5×SSC and 1% SDS at 65° C., bothwith a wash of 0.2×SSC and 0.1% SDS at 65° C. Exemplary stringenthybridization conditions can also include a hybridization in a buffer of40% formamide, 1 M NaCl, and 1% SDS at 37° C., and a wash in 1×SSC at45° C. Alternatively, hybridization to filter-bound DNA in 0.5 M NaHPO₄,7% sodium dodecyl sulfate (SDS), 1 mM EDTA at 65° C., and washing in0.1×SSC/0.1% SDS at 68° C. can be employed. Yet additional stringenthybridization conditions include hybridization at 60° C. or higher and3×SSC (450 mM sodium chloride/45 mM sodium citrate) or incubation at 42°C. in a solution containing 30% formamide, 1M NaCl, 0.5% sodiumsarcosine, 50 mM MES, pH 6.5. Those of ordinary skill will readilyrecognize that alternative but comparable hybridization and washconditions can be utilized to provide conditions of similar stringency.

In certain embodiments, the stringency of the wash conditions sets forththe conditions that determine whether a nucleic acid is specificallyhybridized to a surface bound nucleic acid. Wash conditions used toidentify nucleic acids may include (e.g., a salt concentration of about0.02 molar at pH 7 and a temperature of at least about 50° C. or about55° C. to about 60° C.; or, a salt concentration of about 0.15 M NaCl at72° C. for about 15 minutes; or, a salt concentration of about 0.2×SSCat a temperature of at least about 50° C. or about 55° C. to about 60°C. for about 15 to about 20 minutes; or, the hybridization complex iswashed twice with a solution with a salt concentration of about 2×SSCcontaining 0.1% SDS at room temperature for 15 minutes and then washedtwice by 0.1×SSC containing 0.1% SDS at 68° C. for 15 minutes; or,equivalent conditions). Stringent conditions for washing can also be(e.g., 0.2×SSC/0.1% SDS at 42° C.).

A specific example of stringent assay conditions is rotatinghybridization at 65° C. in a salt based hybridization buffer with atotal monovalent cation concentration of 1.5 M (e.g., as described inU.S. patent application Ser. No. 09/655,482 filed on Sep. 5, 2000, thedisclosure of which is herein incorporated by reference) followed bywashes of 0.5×SSC and 0.1×SSC at room temperature.

Stringent assay conditions are hybridization conditions that are atleast as stringent as the above representative conditions, where a givenset of conditions are considered to be at least as stringent ifsubstantially no additional binding complexes that lack sufficientcomplementarity to provide for the desired specificity are produced inthe given set of conditions as compared to the above specificconditions, where by “substantially no more” is meant less than about5-fold more, typically less than about 3-fold more. Other stringenthybridization conditions are known in the art and may also be employed,as appropriate.

The term “salts” herein refers to both salts of carboxyl groups and toacid addition salts of amino groups of the polypeptides of the presentdisclosure. Salts of a carboxyl group may be formed by methods known inthe art and include inorganic salts, for example, sodium, calcium,ammonium, ferric or zinc salts, and the like, and salts with organicbases as those formed, for example, with amines, such astriethanolamine, arginine or lysine, piperidine, procaine and the like.Acid addition salts include, for example, salts with mineral acids suchas, for example, hydrochloric acid or sulfuric acid, and salts withorganic acids such as, for example, acetic acid or oxalic acid. Any ofsuch salts should have substantially similar activity to the peptidesand polypeptides of the present disclosure or their analogs.

The polynucleotides and the vectors can be introduced into cells withdifferent purposes, generating transgenic cells and organisms. A processfor producing cells capable of expressing a polypeptide of the presentdisclosure includes genetically engineering cells with such vectors andnucleic acids.

In particular, host cells (e.g., bacterial cells) can be modified bytransformation for allowing the transient or stable expression of thepolypeptides encoded by the nucleic acids and the vectors of the presentdisclosure. Alternatively the molecules can be used to generatetransgenic animal cells or non-human animals (by non-/homologousrecombination or by any other method allowing their stable integrationand maintenance), having enhanced or reduced expression levels of thepolypeptides of the present disclosure, when the level is compared withthe normal expression levels. Such precise modifications can be obtainedby making use of the nucleic acids of the present disclosure and oftechnologies associated, for example, to gene therapy (Meth. Enzymol.,vol. 346, 2002) or to site-specific recombinases (Kolb A F, 2002).

Gene silencing approaches may also be undertaken to down-regulateendogenous expression of a gene encoding a polypeptide of the presentdisclosure. RNA interference (RNAI) (Elbashir, S M et al., Nature 2001,411, 494-498) is one method of sequence specific post-transcriptionalgene silencing that may be employed. Short dsRNA oligonucleotides aresynthesised in vivo and introduced into a cell. The sequence specificbinding of these dsRNA oligonucleotides triggers the degradation oftarget mRNA, reducing or ablating target protein expression.

Efficacy of the gene silencing approaches assessed above may be assessedthrough the measurement of polypeptide expression (for example, byWestern blotting), and at the RNA level using TaqMan-basedmethodologies.

The polypeptides of the present disclosure can be prepared by any methodknown in the art, including recombinant DNA-related technologies, andchemical synthesis technologies. In particular, a method for making apolypeptide of the present disclosure may include culturing a host ortransgenic cell as described above under conditions in which the nucleicacid or vector is expressed, and recovering the polypeptide encoded bysaid nucleic acid or vector from the culture. For example, when thevector expresses the polypeptide as a fusion protein with anextracellular or signal-peptide containing proteins, the recombinantproduct can be secreted in the extracellular space, and can be moreeasily collected and purified from cultured cells in view of furtherprocessing or, alternatively, the cells can be directly used oradministered.

The DNA sequence coding for the proteins of the present disclosure canbe inserted and ligated into a suitable episomal or non-/homologouslyintegrating vectors, which can be introduced in the appropriate hostcells by any suitable means (transformation, transfection, conjugation,protoplast fusion, electroporation calcium phosphate-precipitation,direct microinjection, etc.). Factors of importance in selecting aparticular plasmid or viral vector include: the ease with whichrecipient cells that contain the vector may be recognized and selectedfrom those recipient cells which do not contain the vector; the numberof copies of the vector which are desired in a particular host; andwhether it is desirable to be able to “shuttle” the vector between hostcells of different species.

The vectors should allow the expression of the isolated or fusionprotein including the polypeptide of the disclosure in the prokaryoticor eukaryotic host cells under the control of transcriptionalinitiation/termination regulatory sequences, which are chosen to beconstitutively active or inducible in the host cell. A cell linesubstantially enriched in such cells can be then isolated to provide astable cell line.

For eukaryotic hosts (e.g., yeasts, insect plant, or mammalian cells),different transcriptional and translational regulatory sequences may beemployed, depending on the nature of the host. They may be derived formviral sources, such as adenovirus, bovine papilloma virus, Simian virusor the like, where the regulatory signals are associated with aparticular gene, which has a high level of expression. Examples are theTK promoter of the Herpes virus, the SV40 early promoter, the yeast gal4gene promoter, etc. Transcriptional initiation regulatory signals may beselected which allow for repression and activation, so that expressionof the genes can be modulated. The cells stably transformed by theintroduced DNA can be selected by introducing one or more markersallowing the selection of host cells which contain the expressionvector. The marker may also provide for prototrophy to an auxotropichost biocide resistance, e.g., antibiotics, or heavy metals such ascopper, or the like. The selectable marker gene can either be directlylinked to the DNA gene sequences to be expressed, or introduced into thesame cell by co-transfection.

Host cells may be either prokaryotic or eukaryotic. Preferred areeukaryotic hosts, e.g., mammalian cells, such as human, monkey, mouse,and Chinese Hamster Ovary (CHO) cells, because they providepost-translational modifications to proteins, including correct foldingand glycosylation. Also yeast cells can carry out post-translationalpeptide modifications including glycosylation. A number of recombinantDNA strategies exist that utilize strong promoter sequences and highcopy number of plasmids, which can be utilized for production of thedesired proteins in yeast. Yeast recognizes leader sequences in clonedmammalian gene products and secretes peptides bearing leader sequences(i.e., pre-peptides).

“Contacting” means to bring or put together. As such, a first item iscontacted with a second item when the two items are brought or puttogether (e.g., by touching them to each other).

As used herein, the term “organelle” refers to cellular membrane-boundstructures such as the chloroplast, mitochondrion, and nucleus. The term“organelle” includes natural and synthetic organelles.

As used herein, the term “non-nuclear organelle” refers to any cellularmembrane bound structure present in a cell, except the nucleus.

As used herein, the term “host” or “organism” includes humans, mammals(e.g., cats, dogs, horses, etc.), living cells, and other livingorganisms. A living organism can be as simple as, for example, a singleeukaryotic cell or as complex as a mammal.

Discussion

Polypeptides (luciferases) having modulated properties, as well as thepolynucleotides encoding the same, are provided. In representativeembodiments, the luciferases exhibit at least one of modulatedstability, enhanced light output, and modulated emission maximum. Alsoprovided are fragments of the subject polynucleotides and the subjectpolypeptides encoded thereby, as well as antibodies to the subjectpolypeptides and transgenic cells and organisms. In addition, fusionproteins including the subject polypeptides or portions thereof and thesubject polynucleotides encoding the same are provided. The subjectpolynucleotide and/or polypeptide compositions find use in a variety ofdifferent applications as discussed below. In addition, kits for use insuch applications (e.g., kits that include the subject polynucleotideand/or subject polypeptide compositions) are provided.

Embodiments of the present disclosure can be used in systems to detectcellular events, such as, but not limited to, protein-proteininteractions, protein dimerization, protein phosphorylation, caspasedetection, and/or cellular ion exchange. In addition, the embodiments ofthe present disclosure can be used to detect (and visualize) andquantitate cellular events in vitro as well as in vivo. Embodiments ofthe polynucleotides and polypeptides can be used as bioluminescent donorproteins, reporter proteins, split reporter proteins, oxygen sensors,activatable proteins, and the like. Embodiments of the presentdisclosure can be used in bioluminescence resonance energy transfer(BRET) systems, protein interaction detection systems, systems where theprotein is activated by another protein (e.g., caspase ormatrix-metalloprotease activatable), the monitoring of gene regulatorysystems, and the like.

In further describing the subject disclosure, the subject polynucleotidecompositions will be described first, followed by a discussion of thesubject polypeptide compositions, antibody compositions, fusionpolypeptides, and transgenic cells/organisms. Next a review ofrepresentative methods in which the subject proteins find use isprovided.

Polynucleotide Compositions

Embodiments of the present disclosure provide mutant polynucleotides(also referred to as nucleic acid or polynucleotide compositions)encoding mutant luciferases (also referred to as “polypeptides”), aswell as fragments and homologues of these polypeptides.

As used herein, luciferases refer to oxygenases that catalyze a lightemitting reaction, and luciferin refers to a substrate that iscatabolized in the reaction by the given luciferase. For instance,bacterial luciferases catalyze the oxidation of flavin mononucleotide(FMN) and aliphatic aldehydes, which reaction produces light. Anotherclass of luciferases, found among marine arthropods, catalyzes theoxidation of Cypridina (Vargula) luciferin, and another class ofluciferases catalyzes the oxidation of Coleoptera luciferin. Thus,luciferase refers to an enzyme or photoprotein that catalyzes abioluminescent reaction (a reaction that produces bioluminescence). Theluciferases, such as Coleoptera and Renilla luciferases, are enzymesthat act catalytically and are unchanged during the bioluminescencegenerating reaction. The luciferase photoproteins, such as the aequorinphotoprotein to which luciferin is non-covalently bound, are changed,such as by release of the luciferin, during bioluminescence generatingreaction. For purposes herein, reference to luciferase refers to eitherthe photoproteins or luciferases.

In Representative embodiments, the mutant luciferase polynucleotides,encoded by the nucleic acids, are mutants of luciferases that include anα/β-hydrolase fold, where this structure may occur at a position rangingfrom about residue 50 to about residue 500 (e.g., from about residue 70to about residue 300 (as numbered from the N-terminal amino acid)). Inrepresentative embodiments, the mutant luciferase polynucleotidesencoded by the nucleic acids are mutants of luciferases that have amolecular weight which is less than the molecular weight of Coleopteraluciferases (e.g., less than about 60 kD, such as less than about 50 kD,less than about 40 kD, and less than about 36 kD). In representativeembodiments, the mutant luciferase polynucleotides encoded by thenucleic acids are mutants of luciferases that exhibit a significantlevel of homology (e.g., from about 30 to 60%, from about 34 to 56%) toa number of different bacterial haloalkane dehalogenases. Inrepresentative embodiments, the mutant luciferase polynucleotidesencoded by the nucleic acids are mutants of luciferase polynucleotidesthat employ a coelenterazine as a substrate, where the termcoelenterazine refers collectively to native coelenterazine, as well asanalogues thereof, where representative coelenterazine analogues ofinterest include, but are not limited to: benzy-coelenterazine;coelenterazine-cp; coelenterazine-n; bisdeoxycoelenterazine; and thelike. Additional details regarding substrates are provided below.

In representative embodiments, the subject luciferase polynucleotidesare mutants of wild-type luciferases found in Cnidarian species (e.g.,an Anthozoan species, such as a Renilla species (e.g., Renillakoellikeri; Renilla muelleri and Renilla reniformis, where inrepresentative embodiments, the mutant luciferase is a mutant of theRenilla reniformis wild-type luciferase)). The subject polynucleotidesand the encoded subject polypeptide sequences of the Renilla reniformiswild-type luciferase are known and reported in Lorenz et al., Proc.Nat'l Acad. Sci. USA (1991) 88:4438-4442 and also reported in U.S. Pat.No. 6,451,549 as SEQ ID NOS: 1 and 2, the disclosure of which is hereinincorporated by reference. In certain embodiments, the subjectpolynucleotides are mutants of a luciferase encoded by a “humanized”version of the wild-type Renilla reniformis luciferase polynucleotidecoding sequence, where the luciferase protein encoded therein includesan amino acid substitution at position 2 from threonine (T) to alanine(A) (also called a T2A substitution).

As mentioned above, the subject polynucleotides encode mutantluciferases. The term “mutant” is employed broadly to refer to a proteinthat differs in some way from a reference wild-type protein, where thesubject protein may retain biological properties of the referencewild-type (e.g., naturally occurring) protein, or may have biologicalproperties that differ from the reference wild-type protein. The term“biological property” of the subject proteins includes, but is notlimited to, spectral properties, such emission maximum, quantum yield,and brightness (e.g., as compared to the wild-type protein or anotherreference protein such as firefly luciferase from P. pyralis), and thelike; in vivo and/or in vitro stability (e.g., half-life); and the like.Mutants of the disclosure include single amino acid changes (pointmutations), deletions of one or more amino acids (point-deletions),N-terminal truncations, C-terminal truncations, insertions, and thelike.

For purposes of the disclosure, a naturally occurring luciferase is areference wild type luciferase for a given mutant if the amino acidsequences of the wild-type and the mutant have high identity over atleast the length of the mutant (e.g., at least about 90%, at least about95%, at least about 97%, at least about 98%, at least about 99% orhigher) but will not have complete sequence identity in representativeembodiments. In representative embodiments, the mutant will be encodedby a polynucleotide that has been derived from a polynucleotide thatencodes the reference wild-type protein (e.g., derived from the wildtype encoding nucleic acid by a targeted mutagenesis approach) where afirst nucleic acid is considered to be derived from a second nucleicacid if, at some time during the development of the first nucleic acid,the second nucleic acid, or at least the sequence information thereof,is used.

Embodiments of the disclosure provide for subject polynucloetides thatencode luciferase mutants that retain luciferase activity (e.g.,catalyze the conversion of a coelenterazine substrate into a luminescentproduct in the presence of molecular oxygen). A feature of embodimentsof the disclosure is that the subject luciferase mutants encoded by thesubject polynucleotide compositions have at least one of the followingproperties relative to their corresponding reference wild-type nucleicacid: modulated stability; enhanced light output; and modulated emissionwavelength maximum. In certain embodiments, the subject mutants includetwo or more of the above properties (e.g., modulated stability andenhanced brightness, enhanced light output and modulated emissionmaximum, modulated stability and modulated emission maximum) or includethree or more of the above properties (e.g., modulated stability,enhanced light output and modulated emission maximum).

In representative embodiments, the subject mutants encoded by thesubject polynucleotides have at least modulated stability as compared totheir corresponding reference wild type protein. Specifically, themutants have at least modulated stability under in vivo conditions ascompared to their corresponding reference wild type. For purposes of thepresent disclosure, modulated stability under in vivo conditions isdetermined by evaluating the activity of a given mutant and itscorresponding reference wild type protein under mammalian (e.g., rat ormouse) serum conditions for a duration of time.

In certain embodiments, a given mutant exhibits enhanced stability,where the magnitude of enhancement may be at least about 50%, at leastabout 75% at least about 80%, at least about 85%, or more (e.g., by atleast about 2-fold or more, by at least about 10-fold or more, by atleast about 50-fold or more, by at least about 150-fold more).

In representative embodiments in which the subject polynucleotidesencode a mutant of Renilla luciferase that exhibits enhanced stability,the encoded mutant may include a point mutation at least one of thefollowing positions: A55; S130; K136, A143; M253, and S287. Specificpoint mutations of interest include, but are not limited to: A55T;S130A; K136R; A143M, M253L, and S287L (SEQ ID NOS: 3-8). In thoseembodiments where a C124 mutation (C124A mutation) is present, theencoded mutant typically further includes at least one additionalmutation, such as one or more of the above additional point mutationsand/or one or more of the light output enhancing and/or emissionwavelength maximum modulating mutations described in greater detailbelow. In certain embodiments, the subject polynucleotides encode amutant that includes two or more of the above mutations, three or moreof the above mutations, four or more of the above mutations, five ormore of the above mutations, or even all of the above mutations, whereadditional mutations may also be present.

In certain embodiments, a given mutant exhibits enhanced lability (i.e.,decreased stability), where the magnitude of enhanced lability may be atleast about 10%, at least about 25% or more, at least about 50% or more(e.g., by at least about 2-fold or more, by at least about 10-fold ormore, by at least about 50-fold or more).

In representative embodiments in which the subject polynucleotidesencode a mutant of Renilla luciferase that exhibits enhanced lability,the encoded mutant may include a point mutation at least one of thefollowing positions: Q235 and S257. Specific point mutations of interestinclude, but are not limited to: Q235A and S257G (SEQ ID NOS: 9-10). Incertain embodiments, the subject polynucleotides encode a mutant thatincludes both the above mutations, where additional mutations may alsobe present.

In representative embodiments, the mutants encoded by the subjectpolynucleotides exhibit increased light output as compared to theircorresponding reference wild type protein. Specifically, the subjectmutants have at least enhanced light output with a given coelenterazinesubstrate as compared to their corresponding reference wild type. Forpurposes of the present disclosure, increased light output is determinedby evaluating at least one of the kinetics and quantum yield of a givenmutant using a convenient assay known to those of skill in the art,where specific assays of interest for determining increased light outputare described in the Examples below.

In certain embodiments, these subject mutants exhibit at least increasedkinetics, where the magnitude of the increase (as compared to areference wild type protein) is, in representative embodiments, at leastabout 25%, at least about 50%, at least about 75% or more (e.g., atleast about 2-fold or more, at least about 25-fold or more, at leastabout 50-fold or more, at least about 100-fold or more).

In certain embodiments, these subject mutants exhibit at least increasedquantum yield for a given coelenterazine substrate, where the magnitudeof the increase (as compared to a reference wild type protein) is, inrepresentative embodiments, at least about 25%, at least about 50%, atleast about 75% or more (e.g., at least about 2-fold or more, at leastabout 25-fold or more, at least about 50-fold or more, at least about100-fold or more).

In representative embodiments in which the subject polynucleotidesencode a mutant of Renilla luciferase that exhibits enhanced lightoutput, the encoded mutant may include a point mutation at least one ofthe following positions: K136; M185, and S287. Specific point mutationsof interest include, but are not limited to: K136R, M185V, and S287L(SEQ ID NOS: 3, 11, and 8). In certain embodiments, the subjectpolynucleotides encode a mutant that includes two or more of the abovemutations, such as all of the above mutations, where additionalmutations may also be present.

In representative embodiments, the mutants encoded by the subjectpolynucleotides provide at least a modulated emission wavelength maximumas compared to their corresponding reference wild type protein.Specifically, the mutants provide at a least modulated wavelengthmaximum for a given coelenterazine substrate as compared to theircorresponding reference wild type protein. For purposes of the presentdisclosure, wavelength emission maximum is determined by any convenientassay known to those of skill in the art, where a specific assay ofinterest for determining wavelength emission maximum of a given mutantis provided in the Examples below.

In certain embodiments, a given mutant exhibits a blue shifted emissionwavelength maximum, by which is meant that the wavelength of theemission maximum is reduced as compared to the reference wild typecontrol, where the magnitude of blue shift may be at least about 5 nm orat least about 10 nm or more (e.g., at least about 15 nm or more and atleast about 20 nm or more).

In representative embodiments in which the subject polynucleotidesencode a mutant of Renilla luciferase that exhibits an emissionwavelength maximum shifted to shorter wavelengths of light (blueshifted), the encoded mutant may include a point mutation in thesubstrate binding pocket (or enzymatic pocket). In certain of theseembodiments, the point mutation is at least one of the followingpositions: N53, A54, D120, W121, V146, F181, and F286. Specific pointmutations of interest include, but are not limited to: N53Q, A54P,D120N, W121F, V1461, V146M, F181W, and F286Y (SEQ ID NOS 31-38). Incertain embodiments, the subject polynucleotides encode a mutant thatincludes two or more of the above mutations, three or more of the abovemutations, four or more of the above mutations, five or more of theabove mutations, six or more of the above mutations, or even all of theabove mutations, where additional mutations may also be present.

In representative embodiments in which the subject polynucleotidesencode a mutant of Renilla luciferase that exhibits shifted wavelengthlight output, the encoded mutant may include red-shifted mutated RenillaLuciferase proteins that have their major radiation peak 15 nm or moretoward longer wavelengths than unmutated Renilla Luciferase proteinswithout excessive (where excessive implies a >95% loss) enzymaticactivity loss, portions thereof, mutants thereof, variants thereof,conservative variants thereof, and the like. Red shifted emission ofphotons is advantageous because the longer wavelength photons canpenetrate tissue better than shorter wavelength photons.

In representative embodiments in which the subject polynucleotidesencode a mutant of Renilla luciferase that exhibits shifted wavelengthlight output, the encoded mutant may include red-shifted mutated RenillaLuciferase proteins that have their major radiation peak at least 15 nmor more toward longer wavelengths than unmutated Renilla Luciferaseproteins without excessive enzymatic activity loss, at least 20 nm ormore toward longer wavelengths than unmutated Renilla Luciferaseproteins without excessive enzymatic activity loss, at least 25 nm ormore toward longer wavelengths than unmutated Renilla Luciferaseproteins without excessive enzymatic activity loss, at least 30 nm ormore toward longer wavelengths than unmutated Renilla Luciferaseproteins without excessive enzymatic activity loss, at least 35 nm ormore toward longer wavelengths than unmutated Renilla Luciferaseproteins without excessive enzymatic activity loss, at least 40 nm ormore toward longer wavelengths than unmutated Renilla Luciferaseproteins without excessive enzymatic activity loss, at least 45 nm ormore toward longer wavelengths than unmutated Renilla Luciferaseproteins without excessive enzymatic activity loss, at least 50 nm ormore toward longer wavelengths than unmutated Renilla Luciferaseproteins without excessive enzymatic activity loss, at least 55 nm ormore toward longer wavelengths than unmutated Renilla Luciferaseproteins, or at least 60 nm or more toward longer wavelengths thanunmutated Renilla Luciferase proteins.

In representative embodiments in which the subject polynucleotidesencode a mutant of Renilla luciferase that exhibits shifted wavelengthlight output, the encoded mutant may include a red-shifted mutatedRenilla Luciferase protein that has its major radiation peak about 15 to60 nm more toward longer wavelengths than unmutated Renilla Luciferaseproteins. In representative embodiments in which the subjectpolynucleotides encode a mutant of Renilla luciferase that exhibitsshifted wavelength light output, the encoded mutant may includered-shifted mutated Renilla Luciferase proteins that have their majorradiation peak about 25 to 50 nm or more toward longer wavelengths thanunmutated Renilla Luciferase proteins without excessive enzymaticactivity loss.

In representative embodiments in which the subject polynucleotidesencode a mutant of Renilla luciferase that exhibits shifted wavelengthlight output, the encoded mutant may include a red-shifted mutatedRenilla Luciferase protein that emits about 5 to 30% of its radiationabove 600 nm, about 6 to 23% of its radiation above 600 nm, about 10 to23% of its radiation above 600 nm, about 15 to 23% of its radiationabove 600 nm, or about 20 to 23% of its radiation above 600 nm.

The red-shifted mutated Renilla Luciferase proteins can include proteinsthat have an amino acid-sequence selected from: SEQ ID NO: 18, SEQ IDNO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQID NO: 24, SEQ ID NO: 25, SEQ ID NO: 26, SEQ ID NO: 27, SEQ ID NO: 28,SEQ ID NO: 29, and SEQ ID NO: 30, portions of each, mutants of each,variants of each, or conservative variants of each.

Table 1 includes some exemplary embodiments of the red-shifted mutatedRenilla Luciferase proteins.

TABLE 1 Activity Red-shift % of (relative to compared to photons nativeRenilla native Renilla above Mutations (SEQ ID NO) luciferase)luciferase (nm) 600 nm RLuc8/I159H (18) 0.05 24 10 RLuc8/I163Y (19) 0.1720 8 RLuc8/F261W (20) 0.26 22 8 RLuc8/F262W (21) 0.75 18 7 RLuc8/I223C(22) 3.9 21 9 RLuc8/F181Y (23) 0.09 15 6 RLuc8/A123S/D162E/I163L 3.8 4112 (24) RLuc8/A123S/D162N/I163L 3.1 25 7 (25) RLuc8/A123S/D162E/ 3.4 5015 I163L/V185L (26) RLuc8/A123S/D154M/ 6.0 53 17 E155G/D162E/I163L/V185L(27) RLuc8/A123S/D154K/E155N/ 1.9 63 21 D162E/I163L/F261W (28)RLuc8/A123S/D154V/E155G/ 1.7 61 21 D162E/I163V/F262W (29)RLuc8/A123S/D154A/E155G/ 1.2 65 23 D162E/I163V/F262W (30) Note: RLuc8 isRLuc with the following mutations: A55T, C124A, S130A, K136R, A143M,M185V, M253L, and S287L (SEQ ID NO: 13).

In representative embodiments in which the subject polynucleotidesencode a mutant of Renilla luciferase that exhibits a red shiftedemission wavelength maximum, the encoded mutant may include a pointmutation in the substrate binding pocket (or enzymatic pocket). Incertain of these embodiments, the point mutation is at least one of thefollowing positions: A123, D154, E155, I159, D162, I163, F181, V185,I223, F261, and/or F262. Specific point mutations of interest include,but are not limited to: A123S, D154A, D154K, D154M, D154V, E155G, E155N,I159F, I159H, I159Y, D162E, D162N, I163H, I163L, I163V, I163W, I163Y,F181Y, M185L, I223C, I223H, I223M, and/or I223Q, F261W, F262W, andF262Y. In certain embodiments, the mutant includes two or more of theabove mutations, such as three or more, four or more, five or more, oreven all of the above mutations, where additional mutations may also bepresent as well.

Specific polynucleotides of interest include those polynucleotides thatencode the specific mutant luciferases of Renilla luciferase (e.g.,Rluc8) (SEQ ID NO: 13).

Subject polynucleotide compositions of the disclosure includecompositions that include a sequence of DNA having an open reading framethat encodes a luciferase polypeptide of the subject disclosure, suchthat the sequence of DNA may be referred to as a luciferase gene, and iscapable, under appropriate conditions, of being expressed as aluciferase protein according to the subject disclosure. Also encompassedin this term are polynucleotides that are homologous, substantiallysimilar, or identical to the polynucleotides of the present disclosure.Thus, embodiments of the disclosure provide genes and coding sequencesthereof encoding the polynucleotides of the subject disclosure, as wellas homologs thereof. The subject polynucleotides, if naturallyoccurring, are present in other than their natural environment (e.g.,they are isolated), and/or present in enriched amounts from theirnaturally occurring environment (e.g., the organism from which they areobtained). Embodiments of the present disclosure include, but are notlimited to, isolated subject polynucleotides, isolated subjectpolypeptides, isolated subject antibodies, isolated subject cells (e.g.,transgenic), and the like.

In addition to the above-described luciferase mutants, additionalluciferase mutants that include at least one of modulated stability,enhanced light output, and modulated wavelength emission maximum arealso encompassed by the disclosure. In representative embodiments, suchmutants or variants have point mutations such as those described abovein analogous or corresponding positions of their sequence with respectto the specific positions identified in the above representativemutants. Analogous or corresponding sequence positions to make pointmutations in a given protein are readily determined by aligning theenclosed specific mutants and the sequences of the wild-type proteinfrom the species of interest, a consensus sequence, as reported in theexperimental section below, to identify appropriate positions forvariation.

In addition to the above-described specific subject polynucleotidecompositions, also of interest are homologues of the above-sequences.With respect to homologues of the subject polynucleotide, the source ofhomologous genes may be any species of plant or animal, or the sequencemay be wholly or partially synthetic. In certain embodiments, sequencesimilarity between homologues is at least about 20%, at least about 25%,and may be 30%, 35%, 40%, 50%, 60%, 70% or higher, including 75%, 80%,85%, 90% and 95% or higher. Sequence similarity is calculated based on areference sequence, which may be a subset of a larger sequence, such asa conserved motif, coding region, flanking region, and the like. Areference sequence will usually be at least about 18 nt long, moreusually at least about 30 nt long, and may extend to the completesequence that is being compared. Algorithms for sequence analysis areknown in the art, such as BLAST, described in Altschul et al. (1990), J.Mol. Biol. 215:403-10 (using default settings, e.g. parameters w=4 andT=17). The sequences provided herein are used for recognizing relatedand homologous nucleic acids in database searches.

Of particular interest in certain embodiments are subjectpolynucleotides of substantially the same length as the coding portionof the published cDNA for Renilla reniformis luciferase (where by“substantially the same length” is meant that any difference in lengthdoes not exceed about 20 number %, does not exceed about 10 number %,and does not exceed about 5 number %) and having sequence identity toany of these sequences of at least about 90%, at least about 95% and atleast about 99% over the entire length of the subject polynucleotide. Inmany embodiments, the subject polynucleotides have a sequence that issubstantially similar or identical to the wild type sequence. By“substantially similar” is meant that sequence identity will generallybe at least about 60%, at least about 75%, and at least about 80, 85,90, or 95%.

Also provided are subject polynucleotides that encode the polypeptideencoded by the above-described subject polynucleotides, but differ insequence from the above-described nucleic acids due to the degeneracy ofthe genetic code. Also provided are subject polynucleotides thathybridize to the above-described subject polynucleotide under stringentconditions.

The subject polynucleotides can be generated using any convenientprotocol. Mutant polynucleotides can be generated by random mutagenesisor targeted mutagenesis, using well-known techniques that are known inthe art. In some embodiments, homologue or mutant polynucleotides encodemutant luciferases with altered spectral properties, as described inmore detail herein.

Subject polynucleotides of the subject disclosure may be cDNA of genomicDNA or fragments thereof. In certain embodiments, the subjectpolynucleotides of the subject disclosure include one or more of theopen reading frames encoding specific luciferases, and introns, as wellas adjacent 5′ and 3′ non-coding nucleotide sequences involved in theregulation of expression, up to about 20 kb beyond the coding region,but possibly further in either direction. The subject polynucleotidesmay be introduced into an appropriate vector for extrachromosomalmaintenance or for integration into a host genome, as described ingreater detail below.

The term “cDNA” as used herein is intended to include allpolynucleotides that share the arrangement of sequence elements found innative mature mRNA species, where sequence elements are exons and 5′ and3′ non-coding regions. Normally mRNA species have contiguous exons, withthe intervening introns, when present, being removed by nuclear RNAsplicing, to create a continuous open reading frame encoding thepolypeptide.

A genomic sequence of interest includes the subject polynucleotidespresent between the initiation codon and the stop codon, as defined inthe listed sequences, including all of the introns that are normallypresent in a native chromosome. It may further include 5′ and 3′un-translated regions found in the mature mRNA. It may further includespecific transcriptional and translational regulatory sequences, such aspromoters, enhancers, and the like, including about 1 kb, but possiblymore, of flanking genomic DNA at either the 5′ or 3′ end of thetranscribed region. The genomic DNA may be isolated as a fragment of 100kbp or smaller; and substantially free of flanking chromosomal sequence.The genomic DNA flanking the coding region, either 3′ or 5′, or internalregulatory sequences as sometimes found in introns, contains sequencesrequired for proper tissue and stage specific expression.

The subject polynucleotide compositions may encode all or a part of thesubject proteins. Double or single stranded fragments may be obtainedfrom the DNA sequence by chemically synthesizing oligonucleotides inaccordance with conventional methods, by restriction enzyme digestion,by PCR amplification. For the most part, DNA fragments will be of atleast about 15 nt, at least about 18 nt or about 25 nt, and at leastabout 50 nt. In some embodiments, the polynucleotide molecules may beabout 100 nt, about 200 nt, about 300 nt, about 400 nt, about 500 nt,about 600 nt, about 700 nt, or about 720 nt in length. The subjectpolynucleotides may encode fragments of the polypeptides or thefull-length polypeptides (e.g., the subject polynucleotides may encodepolypeptides of about 25 aa, about 50 aa, about 75 aa, about 100 aa,about 125 aa, about 150 aa, about 200 aa, about 210 aa, about 220 aa,about 230 aa, or about 240 aa, up to the entire protein). Inrepresentative embodiments, polynucleotides of interest include at leasta sufficient amount of the parent nucleic acid to retain at least someluciferase activity, such that the fragment encodes a product that hasluciferase activity.

In representative embodiments, the subject polynucleotides are isolatedand obtained in substantial purity, generally as other than an intactchromosome. Usually, the DNA will be obtained substantially free ofother polynucleotide sequences that do not include a polynucleotides orfragment thereof, generally being at least about 50% to at least about90% pure or more and are typically “recombinant” (e.g., flanked by oneor more nucleotides with which it is not normally associated on anaturally occurring chromosome).

The polynucleotides of the corresponding cDNA, the full-length gene, andconstructs of the subject polynucleotides are provided. These moleculescan be generated synthetically by a number of different protocols knownto those of skill in the art. Appropriate polynucleotide constructs arepurified using standard recombinant DNA techniques as described in, forexample, Sambrook et al., Molecular Cloning: A Laboratory Manual, 2ndEd., (1989) Cold Spring Harbor Press, Cold Spring Harbor, N.Y., andunder current regulations described in United States Dept. of HHS,National Institute of Health (NIH) Guidelines for Recombinant DNAResearch, which are both incorporated herein by reference.

Also provided are polynucleotides that encode fusion proteins of thesubject polypeptides, or fragments thereof, which are fused to a secondprotein (e.g., a degradation sequence, a signal peptide, an antibody orbinding fragment/mimetic thereof, and a ligand of interest). As such,fusion proteins may include a subject polypeptide, or fragment thereof,and a non-Anthozoan polypeptide (“the fusion partner”) fused in-frame atthe N-terminus and/or C-terminus of the subject polypeptide. Fusionpartners include, but are not limited to, polypeptides that can bindantibodies specific to the fusion partner (e.g., epitope tags);antibodies or binding fragments thereof; polypeptides that provide acatalytic function or induce a cellular response; ligands or receptorsor mimetics thereof; and the like. In such fusion proteins, the fusionpartner is generally not naturally associated with the subjectluciferase portion of the fusion protein, and is typically not aluciferase protein or derivative/fragment thereof (e.g., it is not foundin Cnidarian or at least Anthozoan species).

In certain embodiments, the fusion partner of a fusion protein of thesubject disclosure is a targeting moiety, where by “targeting moiety” ismeant a moiety that binds specifically to a target molecule of interest.The target molecule of interest can be any of a number of molecules,including but not limited to, a protein/polypeptide, a carbohydrate, alipid, or a nucleic acid. In certain embodiments, the targeting moietyis specific for a target molecule that is present on the surface of acell of interest (e.g., a cell surface moiety). In some of theseembodiments, the cell surface moiety to which the targeting moiety bindsis a cell surface expressed protein. For example, if the cell surfaceprotein of interest is a receptor that binds specifically to a ligand,then a targeting moiety of a fusion protein of the present disclosurecould be that ligand (or the receptor-binding portion thereof). As isevident to one of skill in the art, targeting moieties that find use inthe fusion proteins of the of the present disclosure can be specific fora wide variety of molecules present on the surface of a cell for which aspecific binding partner is known, and as such, no limitation in thisregard is intended.

Also provided are constructs that include the subject polynucleotidesinserted into a vector, where such constructs may be used for a numberof different applications, including propagation, protein production,and the like. Viral and non-viral vectors may be prepared and used,including plasmids. The choice of vector will depend on the type of cellin which propagation is desired and the purpose of propagation. Certainvectors are useful for amplifying and making large amounts of thedesired DNA sequence. Other vectors are suitable for expression in cellsin culture. Still other vectors are suitable for transfer and expressionin cells in a whole animal or person. The choice of appropriate vectoris well within the skill of the art. Many such vectors are availablecommercially. To prepare the constructs, the partial or full-lengthpolynucleotide is inserted into a vector typically by means of DNAligase attachment to a cleaved restriction enzyme site in the vector.Alternatively, the desired nucleotide sequence can be inserted byhomologous recombination in vivo. Typically this is accomplished byattaching regions of homology to the vector on the flanks of the desirednucleotide sequence. Regions of homology are added by ligation ofoligonucleotides, or by polymerase chain reaction using primerscomprising both the region of homology and a portion of the desirednucleotide sequence, for example.

Also provided are expression cassettes or systems that find use in,among other applications, the synthesis of the subject proteins. Forexpression, the gene product encoded by a polynucleotide of thedisclosure is expressed in any convenient expression system, including,for example, bacterial, yeast, insect, amphibian and mammalian systems.In the expression vector, a subject polynucleotide is linked to aregulatory sequence as appropriate to obtain the desired expressionproperties. These regulatory sequences can include promoters (attachedeither at the 5′ end of the sense strand or at the 3′ end of theantisense strand), enhancers, terminators, operators, repressors, andinducers. The promoters can be regulated or constitutive. In somesituations it may be desirable to use conditionally active promoters,such as tissue-specific or developmental stage-specific promoters. Theseare linked to the desired nucleotide sequence using the techniquesdescribed above for linkage to vectors. Any techniques known in the artcan be used. In other words, the expression vector will provide atranscriptional and translational initiation region, which may beinducible or constitutive, where the coding region is operably linkedunder the transcriptional control of the transcriptional initiationregion, and a transcriptional and translational termination region.These control regions may be native to the subject species from whichthe subject nucleic acid is obtained, or may be derived from exogenoussources.

Expression vectors generally have convenient restriction sites locatednear the promoter sequence to provide for the insertion of nucleic acidsequences encoding heterologous proteins. A selectable marker operativein the expression host may be present. Expression vectors may be usedfor, among other things, the production of fusion proteins, as describedabove.

Expression cassettes may be prepared including a transcriptioninitiation region, the gene or fragment thereof, and a transcriptionaltermination region. Of particular interest is the use of sequences thatallow for the expression of functional epitopes or domains of theencoded polypeptide, usually at least about 8 amino acids in length, atleast about 15 amino acids in length, to about 25 amino acids, and up tothe complete open reading frame of the gene. After introduction of theDNA, the cells containing the construct may be selected by means of aselectable marker, the cells expanded and then used for expression.

The above described expression systems may be employed with prokaryotesor eukaryotes in accordance with conventional uses, depending upon thepurpose for expression. For large scale production of the protein, aunicellular organism, such as E. coli, B. subtilis, S. cerevisiae,insect cells in combination with baculovirus vectors, or cells of ahigher organism such as vertebrates (e.g., COS 7 cells, HEK 293, CHO,Xenopus Oocytes, and the like) may be used as the expression host cells.In some situations, it is desirable to express the gene in eukaryoticcells, where the expressed protein will benefit from native folding andpost-translational modifications. Specific expression systems ofinterest include bacterial, yeast, insect cell and mammalian cellderived expression systems. Small peptides can also be synthesized inthe laboratory. Polypeptides that are subsets of the complete proteinsequence may be used to identify and investigate parts of the proteinimportant for function.

When any of the above host cells, or other appropriate host cells ororganisms, are used to replicate and/or express the polynucleotides ornucleic acids of the disclosure, the resulting replicated nucleic acid,RNA, expressed protein or polypeptide, is within the scope of thedisclosure as a product of the host cell or organism. The product isrecovered by any appropriate means known in the art.

Also provided are homologs of the polynucleotides. Homologs areidentified by any of a number of methods. A fragment of the providedcDNA may be used as a hybridization probe against a cDNA library fromthe target organism of interest, where low stringency conditions areused. The probe may be a large fragment, or one or more short degenerateprimers. Nucleic acids having sequence similarity are detected byhybridization under low stringency conditions, for example, they canhybridize at 50° C. and 6×SSC (0.9 M sodium chloride/0.09 M sodiumcitrate), and remain bound when subjected to washing at 55° C. in 1×SSC(0.15 M sodium chloride/0.015 M sodium citrate). Sequence identity maybe determined by hybridization under stringent conditions, for exampleat 50° C. or higher and 0.1×SSC (15 mM sodium chloride/1.5 mM sodiumcitrate). Nucleic acids having a region of substantial identity to theprovided sequences (e.g., allelic variants, genetically altered versionsof the gene, and the like) bind to the provided sequences understringent hybridization conditions. By using probes, particularlylabeled probes of DNA sequences, one can isolate homologous or relatedgenes.

Also provided are small DNA fragments of the subject polynucleotides,which fragments are useful as primers for PCR, hybridization screeningprobes, and the like. Larger DNA fragments (e.g., greater than 100 nt)are useful for production of the encoded polypeptide, as describedherein. For use in geometric amplification reactions, such as geometricPCR, a pair of primers will be used. The exact composition of the primersequences is not critical to the disclosure, but for most applicationsthe primers will hybridize to the subject sequence under stringentconditions, as known in the art. It is preferable to choose a pair ofprimers that will generate an amplification product of at least about 50nt and at least about 100 nt. Algorithms for the selection of primersequences are generally known, and are available in commercial softwarepackages. Amplification primers hybridize to complementary strands ofDNA, and will prime towards each other.

The subject polynucleotides, including flanking promoter regions andcoding regions, may be mutated in various ways known in the art togenerate targeted changes in promoter strength, sequence of the encodedprotein, properties of the encoded protein, including bioluminescentproperties of the encoded protein, and the like. The DNA sequence orprotein product of such a mutation will usually be substantially similarto the sequences provided herein (e.g. will differ by at least onenucleotide or amino acid, respectively) and may differ by at least twobut not more than about ten nucleotides or amino acids. The sequencechanges may be substitutions, insertions, deletions, or a combinationthereof. Deletions may further include larger changes, such as deletionsof a domain or exon (e.g., of stretches of 10, 20, 50, 75, 100, 150 ormore aa residues). Techniques for in vitro mutagenesis of cloned genesare known. Examples of protocols for site specific mutagenesis may befound in Gustin et al. (1993), Biotechniques 14:22; Barany (1985), Gene37:111-23; Colicelli et al. (1985), Mol. Gen. Genet. 199:537-9; andPrentki et al. (1984), Gene 29:303-13. Methods for site specificmutagenesis can be found in Sambrook et al., Molecular Cloning: ALaboratory Manual, CSH Press 1989, pp. 15.3-15.108; Weiner et al.(1993), Gene 126:35-41; Sayers et al. (1992), Biotechniques 13:592-6;Jones and Winistorfer (1992), Biotechniques 12:528-30; Barton et al.(1990), Nucleic Acids Res 18:7349-55; Marotti and Tomich (1989), GeneAnal. Tech. 6:67-70; and Zhu (1989), Anal Biochem 177:120-4. Suchmutated nucleic acid derivatives may be used to study structure-functionrelationships of a particular bioluminescent protein, or to alterproperties of the protein that affect its function or regulation.

Also of interest are humanized versions of the subject polynucleotides.As used herein, the term “humanized” refers to changes made to thenucleic acid sequence to optimize the codons for expression of theprotein in human cells (Yang et al., Nucleic Acids Research 24 (1996),4592-4593). See also U.S. Pat. No. 5,795,737 that describes humanizationof proteins, the disclosure of which is herein incorporated byreference.

Protein/Polypeptide Compositions

Embodiments of the present disclosure include mutant luciferasepolypeptides (also called “subject polypeptides” that are encoded by thesubject polynucleotides described herein), as well as subjectpolypeptide compositions related thereto. The terms polypeptide,protein, and polypeptide composition as used herein refer to thefull-length protein as well as portions or fragments thereof. Alsoincluded in these terms are variations of the naturally occurringprotein, where such variations are homologous or substantially similarto the naturally occurring protein, and mutants of the naturallyoccurring proteins, as described in greater detail below. The subjectpolypeptides are present in other than their natural environment.Features of embodiments of the mutant luciferase polypeptides aredescribed above in reference to the subject polynucleotides.

Homologs or polypeptides (or fragments thereof) that vary in sequencefrom amino acid sequences of the above specified mutants of the subjectdisclosure are also provided. By homolog is meant a polypeptide havingat least about 10%, at least about 20% and at least about 30%, and inmany embodiments at least about 35%, at least about 40%, at least about60%, at least about 65%, at least about 70%, at least about 75%, atleast about 80%, at east about 85%, and at least about 90% or higher,amino acid sequence identity to the peptide of the subject disclosure,as determined using MegAlign, DNAstar (1998) clustal algorithm asdescribed in D. G. Higgins and P. M. Sharp, “Fast and Sensitive multipleSequence Alignments on a Microcomputer,” (1989) CABIOS, 5: 151-153,which is hereby incorporated by reference. (Parameters used are ktuple1, gap penalty 3, window, 5 and diagonals saved 5).

Also provided are polypeptides that are substantially identical to thespecifically described subject polypeptides herein, where bysubstantially identical is meant that the polypeptide has an amino acidsequence identity to the subject polypeptide of at least about 60%, atleast about 65%, at least about 70%, at least about 75%, at least about80%, at least about 85%, at least about 90%, and at least about 95%,where in some instances the identity may be higher.

In representative embodiments, the subject homologues have structuralfeatures found in the above provided specific sequences, where suchstructural features include the α/β-hydrolase fold; a size that does notexceed about 40 kD, and the like.

Proteins that are mutants of the specifically described subject proteinsherein are also provided. Mutants may retain biological properties ofthe parent (e.g., naturally occurring) proteins, or may have biologicalproperties that differ from the wild-type proteins. The term “biologicalproperty” of the subject proteins includes, but is not limited to,spectral properties, such as absorbance maximum, emission maximum,maximum extinction coefficient, brightness of the product produced bythe activity of the mutant, and the like; in vivo and/or in vitrostability (e.g., half-life); and the like. Mutants include single aminoacid changes, deletions of one or more amino acids, N-terminaltruncations, C-terminal truncations, insertions, and the like.

Mutants can be generated using standard techniques of molecular biology(e.g., random mutagenesis and targeted mutagenesis). Several mutants aredescribed herein. Given the guidance provided in the Examples, and usingstandard techniques, those skilled in the art can readily generate awide variety of additional mutants and test whether a biologicalproperty has been altered. For example, luminescence intensity can bemeasured using a spectrophotometer at various emission wavelengths.

The subject polypeptides of the present disclosure that are naturallyoccurring proteins are present in a non-naturally occurring environment(e.g., are separated from their naturally occurring environment). Incertain embodiments, the subject proteins are present in a compositionthat is enriched for the subject protein as compared to its naturallyoccurring environment. For example, purified protein is provided, whereby “purified” is meant that the protein is present in a composition thatis substantially free of non-chromo/fluoroprotein proteins of interest,where by “substantially free” is meant that less than 90%, less than60%, and/or less than 50% of the composition is made up ofnon-luciferase mutants of interest. The polypeptides of the subjectdisclosure may also be present as an isolate, by which is meant that thepolypeptide is substantially free of other proteins and other naturallyoccurring biologic molecules, such as oligosaccharides, polynucleotidesand fragments thereof, and the like, where the term “substantially free”in this instance indicates that less than 70%, less than 60%, and/orless than 50% of the composition containing the isolated protein is someother naturally occurring biological molecule. In certain embodiments,the proteins are present in substantially pure form, where by“substantially pure form” is meant at least 95%, at least 97%, and atleast 99% pure.

In addition to the specifically described subject polypeptides,polypeptides that vary from these subject polypeptides (e.g., the mutantproteins described above) are also provided. Generally such polypeptidesinclude an amino acid sequence encoded by an open reading frame (ORF) ofthe gene encoding the subject wild type protein, including the fulllength protein and fragments thereof, particularly biologically activefragments and/or fragments corresponding to functional domains, and thelike; and including fusions of the subject polypeptides to otherproteins or parts thereof. Fragments of interest will typically be atleast about 10 aa in length, at least about 50 aa in length, and may beas long as 300 aa in length or longer, but will usually not exceed about1000 aa in length, where the fragment will have a stretch of amino acidsthat is identical to the subject protein of at least about 10 aa, and atleast about 15 aa, and in many embodiments at least about 50 aa inlength. In some embodiments, the subject polypeptide fragments are about25 aa, about 50 aa, about 75 aa, about 100 aa, about 125 aa, about 150aa, about 200 aa, about 210 aa, about 220 aa, about 230 aa, or about 240aa in length, up to the entire polypeptide. In some embodiments, apolypeptide fragment retains all or substantially all of a biologicalproperty of the wild-type protein.

The subject proteins and polypeptides may be obtained from naturallyoccurring sources or synthetically produced. For example, wild typeproteins may be derived from biological sources that express theproteins (e.g., bioluminescent Cnidarian, e.g., Anthozoan, species) suchas the specific sources listed above. The subject polypeptides may alsobe derived from synthetic methods (e.g., by expressing a recombinantgene or nucleic acid coding sequence encoding the protein of interest ina suitable host) as described above. Any convenient protein purificationprocedures may be employed, where suitable protein purificationmethodologies are described in Guide to Protein Purification, (Deuthsered.) (Academic Press, 1990). For example, a lysate may be prepared fromthe original source and purified using HPLC, exclusion chromatography,gel electrophoresis, affinity chromatography, and the like.

Antibody Compositions

Also provided are antibodies that specifically bind to the subjectbioluminescent proteins. Suitable antibodies are obtained by immunizinga host animal with peptides comprising all or a portion of the subjectprotein(s). Suitable host animals include, but are not limited to,mouse, rat sheep, goat, hamster, and rabbit. The origin of the proteinimmunogen will generally be a Cnidarian species, specifically anAnthozoan species, such as a Renilla species. The host animal willgenerally be a different species than the immunogen (e.g., mice).

The immunogen may include the complete polypeptide, or fragments andderivatives thereof. Preferred immunogens comprise all or a part of thepolypeptide, where these residues contain the post-translationmodifications found on the native target protein. Immunogens areproduced in a variety of ways known in the art (e.g., expression ofcloned genes using conventional recombinant methods, isolation fromAnthozoan species of origin, and the like).

For preparation of polyclonal antibodies, the first step is immunizationof the host animal with the target polypeptide, where the targetpolypeptide will preferably be in substantially pure form, e.g.,including less than about 1% contaminant. The immunogen may include thecomplete target polypeptide, of fragments or derivatives thereof. Toincrease the immune response of the host animal, the target polypeptidemay be combined with an adjuvant, where suitable adjuvants include alum,dextran, sulfate, large polymeric anions, oil & water emulsions (e.g.,Freund's adjuvant, Freund's complete adjuvant, and the like). The targetpolypeptide may also be conjugated to synthetic carrier proteins orsynthetic antigens. A variety of hosts may be immunized to produce thepolyclonal antibodies. Such hosts include, but are not limited to,rabbits, guinea pigs, and rodents (e.g., mice, rats, sheep, goats, andthe like). The target polypeptide is administered to the host, usuallyintradermally, with an initial dosage followed by one or more, usuallyat least two, additional booster dosages. Following immunization, theblood from the host will be collected, followed by separation of theserum from the blood cells. The Ig present in the resultant antiserummay be further fractionated using known methods, such as ammonium saltfractionation, DEAE chromatography, and the like.

Monoclonal antibodies are produced by conventional techniques known tothose of skill in the art. Generally, the spleen and/or lymph nodes ofan immunized host animal provide a source of plasma cells. The plasmacells are immortalized by fusion with myeloma cells to produce hybridomacells. Culture supernatant from individual hybridomas is screened usingstandard techniques to identify those producing antibodies with thedesired specificity. Suitable animals for production of monoclonalantibodies to the human protein include, but are not limited to, mouse,rat, hamster, and the like. To raise antibodies against the mouseprotein, the animal will generally be a hamster, guinea pig, rabbit, andthe like. The antibody may be purified from the hybridoma cellsupernatants or ascites fluid by conventional techniques (e.g., affinitychromatography using protein bound to an insoluble support, protein Asepharose, and the like).

The antibody may be produced as a single chain, instead of the normalmultimeric structure. Single chain antibodies are described in Jost etal. (1994) J.B.C. 269:26267-73, and others. DNA sequences encoding thevariable region of the heavy chain and the variable region of the lightchain are ligated to a spacer encoding at least about 4 amino acids ofsmall neutral amino acids, including glycine and/or serine. The proteinencoded by this fusion allows assembly of a functional variable regionthat retains the specificity and affinity of the original antibody.

Also of interest in certain embodiments are humanized antibodies.Methods of humanizing antibodies are known in the art. The humanizedantibody may be the product of an animal having transgenic humanimmunoglobulin constant region genes (see for example InternationalPatent Applications WO 90/10077 and WO 90/04036), which are incorporatedherein by reference. Alternatively, the antibody of interest may beengineered by recombinant DNA techniques to substitute the CH1, CH2,CH3, hinge domains, and/or the framework domain with the correspondinghuman sequence (see WO 92/02190).

The use of Ig cDNA for construction of chimeric immunoglobulin genes isknown in the art (Liu et al. (1987) P.N.A.S. 84:3439 and (1987) J.Immunol. 139:3521, which are incorporated herein by reference). mRNA isisolated from a hybridoma or other cell producing the antibody and usedto produce cDNA. The cDNA of interest may be amplified by the polymerasechain reaction using specific primers (U.S. Pat. Nos. 4,683,195 and4,683,202). Alternatively, a library is made and screened to isolate thesequence of interest. The DNA sequence encoding the variable region ofthe antibody is then fused to human constant region sequences. Thesequences of human constant regions genes may be found in Kabat et al.(1991) Sequences of Proteins of Immunological Interest, N.I.H.publication no. 91-3242, which is incorporated herein by reference.Human C region genes are readily available from known clones. The choiceof isotype will be guided by the desired effector functions, such ascomplement fixation, or activity in antibody-dependent cellularcytotoxicity. Preferred isotypes are IgG1, IgG3 and IgG4. Either of thehuman light chain constant regions, kappa, or lambda, may be used. Thechimeric, humanized antibody is then expressed by conventional methods.

Antibody fragments, such as Fv, F(ab′)₂ and Fab may be prepared bycleavage of the intact protein (e.g., by protease or chemical cleavage).Alternatively, a truncated gene is designed. For example, a chimericgene encoding a portion of the F(ab′)₂ fragment would include DNAsequences encoding the CH1 domain and hinge region of the H chain,followed by a translational stop codon to yield the truncated molecule.

Consensus sequences of H and L J regions may be used to designpolynucleotides for use as primers to introduce useful restriction sitesinto the J region for subsequent linkage of V region segments to human Cregion segments. C region cDNA can be modified by site directedmutagenesis to place a restriction site at the analogous position in thehuman sequence.

Expression vectors include plasmids, retroviruses, YACs, EBV derivedepisomes, and the like. A convenient vector is one that encodes afunctionally complete human CH or CL immunoglobulin sequence, withappropriate restriction sites engineered so that any VH or VL sequencecan be easily inserted and expressed. In such vectors, splicing usuallyoccurs between the splice donor site in the inserted J region and thesplice acceptor site preceding the human C region, and also at thesplice regions that occur within the human CH exons. Polyadenylation andtranscription termination occur at native chromosomal sites downstreamof the coding regions. The resulting chimeric antibody may be joined toany strong promoter, including retroviral LTRs, e.g. SV-40 earlypromoter, (Okayama et al. (1983) Mol. Cell. Bio. 3:280), Rous sarcomavirus LTR (Gorman et al. (1982) P.N.A.S. 79:6777), and moloney murineleukemia virus LTR (Grosschedl et al. (1985) Cell 41:885); native Igpromoters, and the like.

Transgenics

The polypeptides can be used to generate transgenic, non-human plants oranimals or site specific gene modifications in cell lines. Transgeniccells of the subject disclosure include one or more polypeptidesaccording to the present disclosure present as a transgene, whereincluded within this definition are the parent cells transformed toinclude the transgene and the progeny thereof. In many embodiments, thetransgenic cells are cells that do not normally harbor or contain thepolypeptides according to the present disclosure. In those embodimentswhere the transgenic cells do naturally contain the subjectpolypeptides, the subject polypeptides will be present in the cell in aposition other than its natural location (e.g., integrated into thegenomic material of the cell at a non-natural location). Transgenicanimals may be made through homologous recombination, where theendogenous locus is altered. Alternatively, a polypeptide construct israndomly integrated into the genome. Vectors for stable integrationinclude plasmids, retroviruses and other animal viruses, YACs, and thelike.

Transgenic organisms of the subject disclosure include cells andmulticellular organisms (e.g., plants and animals) that are endogenousknockouts in which expression of the endogenous gene is at least reducedif not eliminated. Transgenic organisms of interest also include cellsand multicellular organisms (e.g., plants and animals) in which theprotein or variants thereof is expressed in cells or tissues where it isnot normally expressed and/or at levels not normally present in suchcells or tissues.

DNA constructs for homologous recombination include at least a portionof the gene of the present disclosure, where the gene has the desiredgenetic modification(s), and includes regions of homology to the targetlocus. DNA constructs for random integration need not include regions ofhomology to mediate recombination. Conveniently, markers for positiveand negative selection are included. Methods for generating cells havingtargeted gene modifications through homologous recombination are knownin the art. For various techniques for transfecting mammalian cells, seeKeown et al. (1990), Meth. Enzymol. 185:527-537, which is incorporatedherein by reference.

For embryonic stem (ES) cells, an ES cell line may be employed, orembryonic cells may be obtained freshly from a host (e.g., mouse, rat,guinea pig, and the like). Such cells are grown on an appropriatefibroblast-feeder layer or grown in the presence of leukemia inhibitingfactor (LIF). When ES or embryonic cells have been transformed, they maybe used to produce transgenic animals. After transformation, the cellsare plated onto a feeder layer in an appropriate medium. Cellscontaining the construct may be detected by employing a selectivemedium. After sufficient time for colonies to grow, they are picked andanalyzed for the occurrence of homologous recombination or integrationof the construct. Those colonies that are positive may then be used forembryo manipulation and blastocyst injection. Blastocysts are obtainedfrom 4 to 6 week old superovulated females. The ES cells aretrypsinized, and the modified cells are injected into the blastocoel ofthe blastocyst. After injection, the blastocysts are returned to eachuterine horn of pseudopregnant females. Females are then allowed to goto term and the resulting offspring screened for the construct. Byproviding for a different phenotype of the blastocyst and thegenetically modified cells, chimeric progeny can be readily detected.

The chimeric animals are screened for the presence of the modified geneand males and females having the modification are mated to producehomozygous progeny. If the gene alterations cause lethality at somepoint in development, tissues or organs can be maintained as allogeneicor congenic grafts or transplants, or in in vitro culture. Thetransgenic animals may be any non-human mammal, such as laboratoryanimals, domestic animals, and the like. The transgenic animals may beused in functional studies, drug screening, and the like. Representativeexamples of the use of transgenic animals include those described infra.

Transgenic plants may be produced in a similar manner. Methods ofpreparing transgenic plant cells and plants are described in U.S. Pat.Nos. 5,767,367; 5,750,870; 5,739,409; 5,689,049; 5,689,045; 5,674,731;5,656,466; 5,633,155; 5,629,470; 5,595,896; 5,576,198; 5,538,879;5,484,956; the disclosures of which are herein incorporated byreference. Methods of producing transgenic plants are also reviewed inPlant Biochemistry and Molecular Biology (eds Lea & Leegood, John Wiley& Sons)(1993) pp 275-295. In brief, a suitable plant cell or tissue isharvested, depending on the nature of the plant species. As such, incertain instances, protoplasts will be isolated, where such protoplastsmay be isolated from a variety of different plant tissues (e.g., leaf,hypoctyl, root, and the like). For protoplast isolation, the harvestedcells are incubated in the presence of cellulases in order to remove thecell wall, where the exact incubation conditions vary depending on thetype of plant and/or tissue from which the cell is derived. Theresultant protoplasts are then separated from the resultant cellulardebris by sieving and centrifugation. Instead of using protoplasts,embryogenic explants comprising somatic cells may be used forpreparation of the transgenic host. Following cell or tissue harvesting,exogenous DNA of interest is introduced into the plant cells, where avariety of different techniques are available for such introduction.With isolated protoplasts, the opportunity arises for introduction viaDNA-mediated gene transfer protocols, including: incubation of theprotoplasts with naked DNA (e.g., plasmids) including the exogenouscoding sequence of interest in the presence of polyvalent cations (e.g.,PEG or PLO); and electroporation of the protoplasts in the presence ofnaked DNA comprising the exogenous sequence of interest. Protoplaststhat have successfully taken up the exogenous DNA are then selected,grown into a callus, and ultimately into a transgenic plant throughcontact with the appropriate amounts and ratios of stimulatory factors(e.g., auxins and cytokinins). With embryogenic explants, a convenientmethod of introducing the exogenous DNA in the target somatic cells isthrough the use of particle acceleration or “gene-gun” protocols. Theresultant explants are then allowed to grow into chimera plants,cross-bred and transgenic progeny are obtained. Instead of the naked DNAapproaches described above, another convenient method of producingtransgenic plants is Agrobacterium mediated transformation. WithAgrobacterium mediated transformation, co-integrative or binary vectorscomprising the exogenous DNA are prepared and then introduced into anappropriate Agrobacterium strain (e.g., A. tumefaciens). The resultantbacteria are then incubated with prepared protoplasts or tissue explants(e.g., leaf disks, and a callus is produced). The callus is then grownunder selective conditions, selected, and subjected to growth media toinduce root and shoot growth to ultimately produce a transgenic plant.

Methods of Use

The luciferase mutants (subject polynucleotides encoding the mutants andthe subject polypeptides) find use in a variety of differentapplications. Representative uses are described below, where thefollowing described uses are merely representative and are in no waymeant to limit the use of the subject polypeptides to those describedbelow.

The subject polynucleotides and polypeptides of the present disclosure(as well as other components of the subject disclosure described above)find use in a variety of different applications, where such applicationsinclude, but are not limited to, the following.

One representative application of interest is the use of the subjectpolypeptides in bioluminescence resonance energy transfer (BRET)applications. The present disclosure provides for subject polypeptides,subject polynucleotides, a bioluminescence initiating compound, and thelike, that can be used for studying (e.g., detecting, localizing, orquantifying) protein-protein interactions inside a host living cell,tissue, or organ, or a host living organism sing the one or methods. Inthese applications, the subject proteins serve as donor and/or acceptorsin combination with a second fluorescent protein or dye (e.g., afluorescent protein as described in Matz et al., Nature Biotechnology(October 1999) 17:969-973; a green fluorescent protein from Aequoriavictoria or fluorescent mutant thereof (e.g., as described in U.S. Pat.Nos. 6,066,476; 6,020,192; 5,985,577; 5,976,796; 5,968,750; 5,968,738;5,958,713; 5,919,445; 5,874,304, the disclosures of which are hereinincorporated by reference); and other fluorescent dyes, e.g., coumarinand its derivatives (e.g. 7-amino-4-methylcoumarin, aminocoumarin),bodipy dyes such as Bodipy FL, cascade blue, fluorescein and itsderivatives (e.g., fluorescein isothiocyanate), Oregon green, rhodaminedyes (e.g., texas red, tetramethylrhodamine), eosins and erythrosins,cyanine dyes (e.g., Cy3 and Cy5), macrocyclic chelates of lanthanideions (e.g., quantum dye, etc.), and chemilumescent dyes, including thosedescribed in U.S. Pat. Nos. 5,843,746; 5,700,673; 5,674,713; 5,618,722;5,418,155; 5,330,906; 5,229,285; 5,221,623; 5,182,202; the disclosuresof which are herein incorporated by reference. Specific examples ofwhere BRET assays employing the subject luciferases may be used include,but are not limited to: the detection of protein-protein interactions(e.g., mammalian two-hybrid system, transcription factor dimerization,membrane protein multimerization, multiprotein complex formation, etc.),and as a biosensor for a number of different events where a peptide orprotein covalently links a BRET fluorescent combination including thesubject fluorescent proteins and where the linking peptide or proteinis, e.g., a protease specific substrate (e.g., for caspase mediatedcleavage), a linker that undergoes conformational change upon receivinga signal that increases or decreases BRET (e.g., PKA regulatory domain(cAMP-sensor), phosphorylation, e.g., where there is a phosphorylationsite in the linker, or the linker has binding specificity to thephosphorylated/dephosphorylated domain of another protein, or the linkerhas Ca²⁺ binding domain). Representative BRET applications in which thesubject proteins find use include, but are not limited to, thosedescribed in: U.S. Pat. Nos. 6,436,682 and 6,232,107; as well aspublished U.S. Patent Application Publication Nos. 20040214227;20030203404 and 20030092098; the disclosures of which are hereinincorporated by reference.

The luciferase polypeptides also find use in applications involving theautomated screening of arrays of cells expressing luciferase reportinggroups by using microscopic imaging and electronic analysis. Screeningcan be used for drug discovery and in the field of functional genomics:e.g., where the subject polypeptides are used as markers of whole cellsto detect changes in multicellular reorganization and migration, e.g.,formation of multicellular tubules (blood vessel formation) byendothelial cells, migration of cells through Fluoroblok Insert System(Becton Dickinson Co.), wound healing, neurite outgrowth, and the like.

The subject luciferase polypeptides also find use in high through-putscreening assays. For example, polypeptides according to the subjectdisclosure can be fused with a putative proteolytic signal sequencederived from a protein with shorter half-life, e.g., PEST sequence fromthe mouse ornithine decarboxylase gene, mouse cyclin B1 destruction box,and ubiquitin. For a description of destabilized proteins and vectorsthat can be employed to produce the same, see e.g., U.S. Pat. No.6,130,313; the disclosure of which is herein incorporated by reference.Promoters in signal transduction pathways can be detected usingdestabilized versions of the subject luciferase proteins for drugscreening (e.g., AP1, NFAT, NF-kB, Smad, STAT, p53, E2F, Rb, myc, CRE,ER, GR and TRE, and the like).

The subject polypeptides can be used as second messenger detectors,e.g., by fusing the subject proteins to specific domains: e.g., PKCgammaCa binding domain, PKCgamma DAG binding domain, SH2 domain, and SH3domain.

Secreted forms of the subject polypeptides can be prepared, e.g. byfusing secreted leading sequences (e.g., as described in publishedUnited States Patent Application 20020081644, the disclosure of which isherein incorporated by reference) to the subject polypeptides toconstruct secreted forms of the subject proteins, which in turn can beused in a variety of different applications.

The subject polypeptides also find use as in vivo markers in animals(e.g., transgenic animals). For example, expression of the subjectprotein can be driven by tissue specific promoters, where such methodsfind use in research for gene therapy, e.g., testing efficiency oftransgenic expression, among other applications.

Additional applications of the subject polypeptides include, but are notlimited to: as markers following injection into cells or animals and incalibration for quantitative measurements (luminescence and protein); asmarkers or reporters in oxygen biosensor devices for monitoring cellviability; as markers or labels for animals, pets, toys, food, and thelike.

The subject polypeptides also find use in protease cleavage assays. Forexample, cleavage inactivated luminescence assays can be developed usingthe subject proteins, where the subject proteins are engineered toinclude a protease specific cleavage sequence without destroying theluminescent character of the protein. Upon cleavage of the protein by anactivated protease, luminescence would sharply decrease due to thedestruction of a functional active site. Alternatively, cleavageactivated luminescence can be developed using the subject polypeptides,where the subject proteins are engineered to contain an additionalspacer sequence in close proximity/or inside the active site. Thisvariant would be significantly decreased in its activity, because partsof the functional active site would be divided by the spacer. The spacerwould be framed by two identical protease specific cleavage sites. Uponcleavage via the activated protease the spacer would be cut out and thetwo residual “subunits” of the protein would be able to reassemble togenerate a functional protein. Cleavage activated luminescence couldalso be developed using the subject proteins, where the subject proteinsare engineered to contain another protein on either terminus, with aprotease cleavage site in the linker between the two proteins. Fusionsto the n-terminus of the subject proteins in particular can result inlarge decreases in the enzymatic activity of the subject proteins.Cleavage at the protease specific cleavage site contained within thelinker would split the fusion protein, releasing the subject proteinsand allowing them to regain full activity. All of the above types ofapplications could be developed in assays for a variety of differenttypes of proteases (e.g., caspases).

The subject polypeptides also find use in marking and/or identifyingspecific cell types in vitro and in vivo. For example, fusion proteinsbetween a luciferase of the subject disclosure and a fusion partner thatis a targeting moiety specific for a cell surface molecule (as describedabove in the Nucleic Acids section), can be contacted to the cells to beassayed/screened under conditions that allow binding of the targetingmoiety to the target cell surface molecule (e.g., via specificinteraction between the fusion partner and the target cell surfacemolecule). For in vitro analysis, the fusion protein can be contacted tothe cells by introducing it into the culture media. For in vivoanalysis, the fusion protein can be injected into the subject to thesite of interest (e.g., intravenously or into a tissue or anatomicallocation of interest). Binding of the fusion protein to the cells canthen be visualized by providing a luciferase substrate (e.g.,coelenterazine) to the cells and spatially detecting the photon emissionpattern, even in whole animals. In this way, the presence and/orlocation of cells that express a specific cell surface molecule can beassayed.

In certain embodiments, the cell surface molecule for which a targetingmoiety of a fusion protein is specific is associated with a cellularphenotype of interest. For example, the cell surface molecule ofinterest might be associated with neoplastic, pre-neoplastic ormetastatic cancer cells (e.g., receptors that promote angiogenesis, asdescribed in the Experimental section below), with specific growthpotential of a cell (e.g., a receptor that transduces growth signals),or with a specific developmental stage of a cell (e.g., effector Tcells).

Additional utilities of the subject mutant luciferases include, but arenot limited to, those described in Published U.S. Patent ApplicationSer. Nos. 20050186606; 20050152838; 20050112576; 20050112551;20050095583; 20040219622; 20040214227; 20040209274; 20040209246;20040197855; 20040171099; 20040137454; 20040121365; 20040096924;20040002123; 20030219723; 20030203404; 20030186313; 20030153090;20030092098; 20030066096; 20030059798; 20020192726; 20020150912;20020090659; 20020081644; as well as in U.S. Pat. Nos. 6,451,549;6,436,682; 6,232,107; 6,228,604; 5,418,155 and 5,292,658; thedisclosures of which are herein incorporated by reference.

The antibodies of the subject disclosure, described above, also find usein a number of applications, including the differentiation of thesubject proteins from other bioluminescent proteins.

Bioluminescence Initiating Compound

The subject polypeptides can be used in conjunction with abioluminescence initiating compound to produce a radiation emission. Thebioluminescence initiating compound can include, but is not limited to,coelenterazine, analogs thereof, and functional derivatives thereof.Derivatives of coelenterazine include, but are not limited to,bisdeoxycoelenterazine (also known as coelenterazine 400a,coelenterazine-hh, and deep blue coelenterazine (DBC)),benzyl-coelenterazine (also known as coelenterazine-h),coelenterazine-cp, coelenterazine-f, coelenterazine-fcp,coelenterazine-hcp, coelenterazine-ip, coelenterazine-n,coelenterazine-o, coelenterazine-i, coelenterazine-icp, andcoelenterazine 2-methyl (described in more detail in U.S. Pat. Nos.6,020,192; 5,968,750 and 5,874,304).

In general, coelenterazines are known to luminesce when acted upon by awide variety of bioluminescent proteins, specifically Luciferases.Useful, but non-limiting, coelenterazines are disclosed in U.S. patentapplication Ser. No. 10/053,482, filed Nov. 2, 2001, the disclosurewhich is hereby incorporated by reference in its entirety.Coelenterazines are available from Promega Corporation, Madison, Wis.and from Molecular Probes, Inc., Eugene, Oreg. Coelenterazines may alsobe synthesized as described for example in Shimomura et al., Biochem. J.261: 913-20, 1989; Inouye et al., Biochem. Biophys. Res. Comm. 233:349-53, 1997; and Teranishi et al., Anal. Biochem. 249: 37-43, 1997,which is incorporated herein by reference.

Kits

Also provided by the subject disclosure are kits for use in practicingone or more of the above described applications, where the subject kitstypically include elements for making the subject polypeptides, e.g., aconstruct comprising a vector that includes a coding region for thesubject polypeptide. The subject kit components are typically present ina suitable storage medium, e.g., buffered solution, typically in asuitable container. Also present in the subject kits may be antibodiesto the subject polypeptide. In certain embodiments, the kit comprises aplurality of different vectors each encoding the subject polypeptide,where the vectors are designed for expression in different environmentsand/or under different conditions, e.g., constitutive expression wherethe vector includes a strong promoter for expression in mammalian cells,a promoterless vector with a multiple cloning site for custom insertionof a promoter and tailored expression.

In representative embodiments, the kits further include a substrate forthe luciferase, where in representative embodiments the substrate is acoelenterazine. As reviewed above, the term coelenterazine referscollectively to native coelenterazine, as well as analogues thereof,where representative coelenterazine analogues of interest include, butare not limited to coelenterazine; coelenterazine-cp; coelenterazine-n;and bisdeoxycoelenterazine.

In addition to the above components, the subject kits will furtherinclude instructions for practicing the subject methods. Theseinstructions may be present in the subject kits in a variety of forms,one or more of which may be present in the kit. One form in which theseinstructions may be present is as printed information on a suitablemedium or substrate, e.g., a piece or pieces of paper on which theinformation is printed, in the packaging of the kit, in a packageinsert. Yet another form would be a computer readable medium, e.g.,diskette, CD, and the like, on which the information has been recorded.Yet another form that may be present is a website address which may beused via the internet to access the information at a removed site. Anyconvenient form of instructions may be present in the kits.

EXAMPLES

Now having described the embodiments of the of the present disclosure,in general, examples 1 and 2 describe some additional embodiments of theof the present disclosure. While embodiments of the present disclosureare described in connection with examples 1 and 2 and the correspondingtext and figures, there is no intent to limit embodiments of the presentdisclosure to these descriptions. On the contrary, the intent is tocover all alternatives, modifications, and equivalents included withinthe spirit and scope of embodiments of the present disclosure. Examples1 and 2 are attached to this document. In addition, each of thereferences described in the Examples are hereby included by reference.

Example 1 Generation and Functional Analysis of Renilla LuciferaseMutants

Materials and Methods

Coelenterazine

Coelenterazine was from Prolume (Pinetop, Ariz.). Benzyl-coelenterazine(coelenterazine-h) was a generous gift from Dr. Bruce Bryan.Coelenterazine-n and coelenterazine-cp were from Biotium (Hayward,Calif.). Bisdeoxycoelenterazine (coelenterazine-400a, di-dehydrocoelenterazine, DeepBlueC) was from Perkin Elmer (Boston, Mass.). Thechemical structures of these compounds are shown in FIG. 1.Coelenterazine and the analogs were dissolved in propylene glycol andstored in small aliquots at −80° C.

Luminometer Calibration

Light measurements were made using a Turner 20/20 and later a Turner20/20n luminometer (Turner Designs, Sunnyvale, Calif.). The luminometerswere calibrated to absolute units (photons/s) using the luminol lightstandard performed in dimethyl sulfoxide (DMSO) (Lee, J., Wesley, A. S.,Ferguson, J. F., III, and Seliger, H. H. (1966) in Bioluminescence inProgress (Johnson, F. H. and Haneda, Y., eds.), pp. 35-43, Princeton,N.J.; O'Kane, D. J. and Lee, J. (2000) Methods Enzymol. 305, 87-96). Nocorrections were applied for the spectral sensitivity of theluminometer, as the spectral peak of luminol chemiluminescence in DMSO(486 nm) is close to the spectral peak of Renilla luciferasebioluminescence (482 nm).

Computational Prediction

A PSI-BLAST search (Altschul, S. F., Madden, T. L., SchÃ¤ffer, A. A.,Zhang, J., Zhang, Z., Miller, W., and Lipman, D. J. (1997) Nucl. AcidsRes. 25, 3389-3402), performed using the PredictProtein server (Rost, B.and Liu, J. (2003) Nucl. Acids Res. 31, 3300-3304), identified a numberof sequences homologous to RLuc. An alignment between RLuc and the 9most similar sequences (46% similarity) was then generated using CLUSTALW (Thompson, J. D., Higgins, D. G., and Gibson, T. J. (1994) Nucl. AcidsRes. 22, 4673-4680).

A homology model of RLuc was built with SWISS-MODEL (v3.5) (Schwede, T.,Kopp, J., Guex, N., and Peitsch, M. C. (2003) Nucl. Acids Res. 31,3381-3385) using the default parameters (FIG. 4( a)). In generating thishomology model, SWISS-MODEL utilized several crystal structures of thehaloalkane dehalogenase LinB from Sphingomonas paucimobilis (PDB files1iz8, 1k63, 1k6e, 1iz7, and 1mj5).

Construction of Renilla Luciferase Mutants

The hrluc gene from the plasmid phRL-CMV (Promega, Madison, Wis.) wasused as the initial template for cloning. This gene is a human codonuseage optimized version of rluc, and encodes a protein identical toRLuc with the exception of a T2A substitution. To construct a bacterialexpression plasmid, CR was used to remove the stop codon and to replacethe N-terminal methionine codon with a pelB leader sequence. The pelBleader sequence, consisting of the first 22 codons of the pectate lyaseB gene from Erwinia carotovora (Lei, S. P., Lin, H. C., Wang, S. S.,Callaway, J., and Wilcox, G. (1987) J. Bacteriol. 169, 4379-4383),directs protein expression into the bacterial periplasm and is cleavedfrom the final protein product. Using NcoI and HindIII restrictionsites, the PCR product was inserted into the pBAD/Myc-His A plasmid(Invitrogen, Carlsbad, Calif.), which adds a Myc epitope, a 6×His tag,and a stop codon to the C-terminus of the gene. In some laterconstructs, the plasmid's SalI site was used for insertion in order toremove the Myc epitope from the construct. Site directed mutagenesis wasperformed using a QuikChange II XL kit (Stratagene, La Jolla, Calif.).All constructs and mutations were confirmed by sequencing.

Protein Production and Purification

Protein was produced in E. coli LMG 194 cells grown at 32° C. inTerrific Broth. Cultures were allowed to reach an OD₆₀₀ of 0.7 and werethen induced by addition of L-(+)-Arabinose to a final concentration of0.2%. 12-14 hours later, cells were harvested and the periplasmextracted by osmotic shock (Neu, H. C. and Heppel, L. A. (1965) J. Biol.Chem. 240, 3685-3692).

The periplasmic fraction was brought to the same concentration as thewash buffer (WB: 300 mM NaCl, 20 mM HEPES, 20 mM imidazole, pH 8) usinga 10× stock, and Phenylmethylsulphonylfluoride was added to 1 mM. Thesolution was clarified by 0.2 mm filtration and ran over a nickelaffinity column (Ni-NTA Superflow, Qiagen, Valencia, Calif.). The columnwas washed with WB and eluted with elution buffer (EB: 300 mM NaCl, 20mM HEPES, 250 mM imidazole, pH 8). Protein concentration measurementswere made using the Bradford assay (Bradford, M. (1976) Anal. Biochem.72, 248-254) with human serum albumin (HSA: Baxter HealthcareCorporation, Glendale, Calif.) as the standard. Aliquots were taken atthis point for gel electrophoresis (FIG. 2). To the remainder of theelution, HSA was added to 1% as a carrier protein. All samples werestored at 4° C.

Characterization of Renilla Luciferase Mutants

Luciferase activity was measured by adding 1 ml of sample (diluted asnecessary in EB containing 1% HSA) to 100 ml room temperature 100 mMsodium phosphate buffer (pH 7) (Sørensen, S. P. L. (1909) Biochem. 2.22, 6), manually adding 1 ml of 0.5 mg/ml coelenterazine or analog,manually mixing, and reading for 10 s in a luminometer. The time betweenthe addition of the luciferin and the start of measurement wasapproximately 4 s.

Serum stability measurements were done by mixing 0.5 ml diluteluciferase with either 20 ml mouse serum or 50 ml rat serum(Equitech-Bio, Kerrville, Tex.), placing the sample in a 37° C.incubator, and removing aliquots for activity testing. To calculateserum half-lives, mono-exponential decay curves were fit to the serumstability data using a Nelder/Mead Simplex non-linear least squaresminimization algorithm provided by the Octave numerical programminglanguage. Emission spectra at ambient temperature were measured using aTriax 320 (Horiba Jobin Yvon, Edison, N.J.), which incorporates anoptical grating device with a liquid N₂ cooled CCD detector.

Protein size and monodispersity was confirmed using a Superdex 200analytical grade gel filtration column (GE/Amersham Biosciences,Piscataway, N.J.) followed by in-line multiangle light scattering andrefractive index detectors (DAWN EOS and Optilab DSP, WyattTechnologies, Santa Barbara, Calif.). A dn/dc value of 0.185 mL/g wasassumed in all calculations, and all processing was performed using theASTRA software package (Wyatt Technologies).

For quantum yield measurements, separate 1 ml drops of protein (³2 pm)and substrate (0.2 pm) were placed in a tube, 100 ml of 100 mM sodiumphosphate buffer (pH 7) was injected by the luminometer to mix, and thetotal light output was integrated (generally 5-10 min). Forcoelenterazine-n, the protein amount was increased 10 fold and theacquisition time lengthened to insure the reaction approachedcompletion.

Kinetics

Kinetics were assessed by injecting 100 ml of 100 mM sodium phosphatebuffer (pH 7) containing coelenterazine onto 1 ml of protein (dilutedappropriately in EB containing 1% HSA), and recording the light outputfor 20 min. The final coelenterazine concentrations tested were 118, 24,4.7, 0.94, 0.19, and 0.038 mM. The final luciferase concentrations werein the range of 1-7 pM. Coelenterazine absorbance was corrected for,although this was only significant for the highest concentration (10%attenuation). The values were converted from photons/s to molecules/susing the data from the quantum yield measurements, inverted from fluxunits to mass units via integration, and processed using the magneticcurve fitting program Dynafit (Kuzmic, P. (1996) Anal. Biochem. pp.260-273).

Mammalian Expression

In order to construct mammalian expression vectors, bacterial expressionvectors containing the desired mutations were used as templates for PCR,with primers designed such that the N-terminal pelB sequence would bereplaced by a methionine codon and a C-terminal stop codon would replacethe Myc epitope and 6×His tag. The primers also contained appropriateNheI and HindIII restriction sites to allow insertion of the productinto the pcDNA 3.1 plasmid (Invitrogen). The resultant plasmids weretransiently transfected using SuperFect (Qiagen) into 293T (DuBridge, R.B., Tang, P., Hsia, H. C., Leong, P. M., Miller, J. H., and Calos, M. P.(1987) Mol. Cell. Biol. 7, 379-387) cells growing in 24 well platesfollowing the manufacturer's protocol. The transfection medium wasreplaced with fresh medium after 3 h. At several time points followingthe transfection, cells were lysed using passive lysis buffer (Promega),measured for total protein content using the Bradford assay, andassessed for luciferase activity using coelenterazine in the same manneras described above for bacterially expressed luciferase. Intracellularstability of the luciferases was assessed by adding cycloheximide to thewells at a concentration of 100 g/ml, and lysing cells at several timepoints thereafter. Westerns were run on lysates with a monoclonalantibody to RLuc (MAb 4400, Chemicon, Temecula, Calif.) in orderdetermine the luciferase protein content, with bacterially producedpurified RLuc8 used as the standard.

Results

Computational Predictions for Renilla Luciferase

Via sequence similarity searches, RLuc was predicted to contain acharacteristic α/β-hydrolase fold from around amino acid 71 to 301(Marchler-Bauer, A., Anderson, J. B., DeWeese-Scott, C., Fedorova, N.D., Geer, L. Y., He, S., Hurwitz, D. I., Jackson, J. D., Jacobs, A. R.,Lanczycki, C. J., Liebert, C. A., Liu, C., Madej, T., Marchler, G. H.,Mazumder, R., Nikolskaya, A. N., Panchenko, A., Rao, B. S., Shoemaker,B. A., Simonyan, V., Song, J. S., Thiessen, P. A., Vasudevan, S., Wang,Y., Yamashita, R. A., Yin, J. J., and Bryant, S. H. (2003) Mol AcidsRes. 31, 383-387), and was found to have a high level 1-56% similar) toa number of bacterial haloalkane dehalogenases.

Mutagenesis of Renilla Luciferase and Screening

In the hopes of further enhancing the stability of RLuc beyond thatachieved with the C124A mutation (C152A in (Liu, J. and Escher, A.(1999) Gene 237, 153-159)), a number of further mutations were explored.Candidate mutations were chosen from the alignment data at positionswhere RLuc most clearly diverged from the consensus sequence. Forinstance, the candidate mutation A55T was chosen because RLuc harborsthe aliphatic amino acid alanine at position 55, while all of thedehalogenases harbor a hydroxylic residue of either threonine or serine.Similarly, S287L was chosen as a candidate because RLuc contains ahydroxylic residue at this position, differing from the consensusaliphatic residue. Some of the candidates, such as M253L, are lessobvious. This mutation substitutes an aliphatic residue for anotheraliphatic, but brings the RLuc sequence into consensus with the highlyconserved local sequence near this position.

Complete results with respect to serum stability, activity, and emissionspectra peaks are summarized in Table 2 for 25 initial mutations, on abackground of RLuc with the C124A mutation, along with data from severalother constructs described below. Note that activity was defined as a 10s integration of the light output curve in order to disfavor mutationsthat merely increased the burst value at the expense of total lightoutput.

TABLE 2 Mutations of RLuc altered serum stability and light output.Activity (photons/s/mole enzyme) Sarum τ_(1/2) (h) Wavelength (nm)native bc cp n bdc mouse rat peak mean Native RLuc (3.2 ± 0.3) × 10²²5.4 × 10²² 1.7 × 10²² 8.3 × 10²¹ 5.8 × 10¹⁹ 0.9 0.4 482 497 Activity(relative to RLuc) Initial Mutations C124A 1.2 ± 0.1 0.75 0.79 0.63 0.687.1 ± 0.4 6.6 ± 0.5   482 498 C124A-ΔMyc 1.3 ± 0.1 0.91 1.1 0.87 1.0 4.04.5 481 499 F33R/I34M/C124A 0.15 0.15 0.16 0.12 0.20 0.3 0.3 481 497E44G/C124A 0.94 0.78 0.74 0.66 0.98 2.6 3.3 486 502 A54G/A55G/C124A 0.120.10 0.06 0.15 0.19 2.4 3.0 476 492 A54P/A55T/C124A 0.21 0.15 0.11 0.380.22 119 129 470 483 A54P/C124A 0.05 0.04 0.05 0.08 0.06 14 13 468 482A55T/C124A 1.7 1.2 0.58 1.4 2.4 30 29 486 504 F116L/C124A 1.3 1.0 1.30.88 1.8 11 9.4 486 502 C124A/S130A 1.7 1.4 1.7 1.4 2.6 18 14 482 498C124A/K136R 2.5 ± 0.3 2.1 1.9 1.9 2.6 12 11 482 498 C124A/A143M 1.7 1.30.95 1.5 1.6 30 29 480 497 C124A/F180A 0.02 0.01 0.03 0.01 0.01 1.6 1.6488 504 C124A/M185V 3.4 3.0 15 7.8 44 5.7 3.7 485 500 C124A/M191L 1.10.99 0.97 1.0 1.2 6.5 5.1 480 496 C124A/E195S/P196D 0.12 0.10 0.12 0.100.15 1.0 0.7 482 498 C124A/F199M 0.58 0.44 0.53 0.49 0.46 6.7 6.0 480495 C124A/L203R 0.55 0.55 0.52 0.41 0.43 2.7 2.2 484 501 C124A/G229E0.02 0.01 0.03 0.03 0.01 1.9 1.8 473 490 C124A/Q235A 1.2 1.1 1.1 1.0 1.23.3 3.6 473 489 C124A/M253L 1.9 1.4 l.6 1.6 1.7 15 10 471 488C124A/S257G 1.1 0.95 1.3 1.1 3.0 1.3 1.4 477 493 C124A/F261L/F262L 0.000.00 0.00 0.00 0.00 N/D N/D C124A/F262L 0.03 0.03 0.01 0.06 0.03 5.8 6.4478 495 C124A/S287L 3.9 2.8 3.4 5.0 9.5 28 20 478 496 C124A/M295I 1.0O.83 0.57 0.72 0.86 5.0 4.9 480 497 C124A/K300A 1.1 1.0 1.1 1.0 1.3 3.53.9 481 497 Stabilized Luciferuse RLuc8 4.3 ± 0.2 3.0 5.8 8.8 59 253 ±58  88 ± 12.4 487 503 Active Site Mutations RLuc8/D120A 0.000 0.0010.001 0.003 0.21 >100 >100 N/D RLuc8/D120N 0.023 0.016 0.050 0.345.1 >100 >100 N/D RLuc8/E144A 0.000 0.000 0.000 0.000 0.000 57 13 N/DRLuc8/E144Q 0.000 0.000 0.000 0.000 0.002 >100 >100 N/D RLuc8/H285A0.023 0.020 0.046 0.028 0.20 >100 21 N/D Destabilized Luciferuses M185V4.4 2.6 12 4.1 20 0.8 0.3 N/D M185V/Q235A 4.8 2.7 14 7.1 20 0.5 0.2 N/DActivity values are the result of integrating over 10 s and are not peakburst values. “Native” indicates the native substrate, while “bc”, “cp”,“n”, and “bdc” indicate the analogs benzyl-coelenterazine,coelenterazinecp, coelenterazine-n, and bisdeoxycoelenterazine,respectively. The results for the native enzyme are reported in absoluteunits, while the values for the mutants are reported as relative to thenative enzyme for the given substrate. Bisdeoxycoelenterazine's emissionspectrum is significantly blue shifted from the other substrates, andsince the luminometer's enhanced spectral sensitivity at these shorterwavelengths was not corrected for, the absolute unit values represent anoverestimation of the real values. The wavelength measurements shown arefor native coelenterazine, and the mean and peak wavelengths differ dueto the non-symmetrical distribution of the emission spectrum. C124A-DMycdiffers from C124A in that the Myc epitope introduced by the bacterialexpression plasmid has been removed in order to make it directlycomparable to RLuc8. RLuc8 contains the mutations A55T, C124A, S130A,K136R, A143M, M185V, M253L, and S287L. In cases were a particularprotein was produced, purified, and assayed independently three or moretimes, the standard error of the mean is reported. N/D—Not Determined.

Representative serum stability data and emission spectra are shown inFIGS. 3( a) and 3(b), respectively.

The assayed values for RLuc reported in Table 1 corresponded well withprevious values reported in the literature. In terms of stability underserum like conditions, our reported values for recombinant RLuc(t_(1/2)=0.4-0.9 h) are in line with Liu et al., who reported ahalf-life of 0.6 h for recombinant RLuc in hamster blood at 37° C. (Liu,J., O'Kane, D. J., and Escher, A. (1997) Gene 203, 141-148), as well asLorenz et al. who reported a half-life of 0.5 h for recombinant highionic strength buffer (Lorenz, W. W., Gray, J. P., Cormier, M. J.,Gibson, B. G., and O'Kane, D. J. (1993) in Bioluminescence andChemiluminescence: Status Report, pp. 191-195, 7th InternationalSymposium on Bioluminescence and Chemiluminescence, Banff, Canada). Themeasured emission peak for RLuc with coelenterazine (482 nm)corresponded exactly with a previously published value of 482 nm forRLuc purified directly from Renilla reniformis (Hart, R. C., Matthews,J. C., Hori, K., and Cormier, M. J. (1979) Biochemistry 18, 2204-2210).

Peak light flux from recombinant RLuc was determined to be 1.2±0.210²³photons/s/mole enzyme when in the presence of 24 mM coelenterazine. Ourvalue corresponds acceptably with the value of 6.5×10²² photons/s/moleenzyme reported for RLuc purified directly from Renilla reniformis(Matthews, J. C., Hori, K., and Cormier, M. J. (1977) Biochemistry 16,85-91), and 9×10²² photons/s/mole enzyme reported for recombinant RLuc(Lorenz, W. W., Gray, J. P., Cormier, M. J., Gibson, B. G., and O'Kane,D. J. (1993) in Bioluminescence and Chemiluminescence: Status Report,pp. 191-195, 7th International Symposium on Bioluminescence andChemiluminescence, Banff, Canada).

Combining Mutations for a Stabilized Luciferase

For the purpose of generating a mutant RLuc more appropriate for use asa bioluminescent tag in small animal imaging applications, the initialmutations were judged for serum stability and light output. In all, 7mutations were deemed as having the most favorable properties and werecombined, along with the C124A mutation, into a single proteindesignated as “RLuc8”. The 8 mutations present in RLuc8 are A55T, C124A,S130A, K136R, A143M, M185V, M253L, and S287L (SEQ ID No: 13). Since theMyc epitope was removed during the cloning of RLuc8, a C124A mutant wasconstructed without the Myc epitope to facilitate a valid comparison(C124A-Δmyc). The stability, activity, and spectra peak values for thesetwo enzymes are shown in Table 1. When compared to the native enzyme,RLuc8 exhibited a greater than 4 fold increase in activity, a 150 foldincrease in serum stability, and a small but measurable 5 nm red shiftin the emission spectrum. Compared to the C124A mutant, RLuc8 showed a 3fold increase in activity and at least a 20 fold improvement in murineserum stability.

Light scattering results suggest RLuc8 exists as a monomer in solution,as molar mass moment calculations based on the multiangle scatteringindicate a molecular weight of 33.8 kDa (error: 7%) with a relativelylow polydispersity across the gel filtration elution profile (˜11%).

Quantum Yield and Kinetic Parameters of Mutants

To understand the basis for RLuc8's higher activity, both quantum yieldand kinetic measurements were undertaken. The results shown in Table 3indicated that RLuc8 had a 30% improvement in quantum yield for nativecoelenterazine, and a ˜30 fold increase in quantum yield forbisdeoxycoelenterazine. A Michaelis-Menten model was fit to initialreaction velocity data for coelenterazine concentrations in the range of0.038 to 24 mM. The results for RLuc, the C124A mutant, and RLuc8 wereK_(m)=2.9±1.0, 2.7±0.8, 1.6±0.2, and k_(cat)=3.9±0.4, 4.7±0.4, 4.9±0.1,respectively, with the errors presented representing the formal standarderrors of the fitted parameters. The results for RLuc are roughlyconsistent with a previously published K_(m) value of 2 mM for RLuc inthe presence of benzyl-coelenterazine (Matthews, J. C., Hori, K., andCormier, M. J. (1977) Biochemistry 16, 5217-5220).

TABLE 3 Mutations of RLuc altered quantum yield. Quantum Yield (%)native bc cp n bdc Native RLuc 5.3 ± 0.1  3.2 ± 0.04  4.7 ± 0.03 6.1 ±0.2 (6.1 ± 0.9) × 10⁻³ C124A 5.4 ± 0.3 3.6 ± 0.1 5.2 ± 0.1  6.4 ± 0.01(7.7 ± 0.5) × 10⁻³ A55T/C124A 5.7 ± 0.2 3.9 ± 0.1 4.5 ± 0.1 5.7 ± 0.1(1.0 ± 0.9) × 10⁻³ C124A/S130A 5.3 ± 0.1  3.4 ± 0.04 5.0 ± 0.1 5.9 ± 0.2(6.7 ± 0.3) × 10⁻³ C124A/K136R 5.4 ± 0.1 3.3 ± 0.1 5.1 ± 0.1 6.0 ± 0.1(7.1 ± 0.3) × 10⁻³ C124A/A143M 5.2 ± 0.3 3.5 ± 0.1 4.8 ± 0.1 5.8 ± 0.2(6.3 ± 0.7) × 10⁻³ C124A/M185V 6.9 ± 0.3 6.3 ± 0.1 10.1 ± 0.2  9.4 ± 0.4(174.4 ± 6.7) × 10⁻³  C124A/M253L 5.5 ± 0.1 3.5 ± 0.1 5.1 ± 0.2 5.8 ±0.1 (7.6 ± 0.3) × 10⁻³ C124A/S287L 6.1 ± 0.2 5.0 ± 0.1 7.2 ± 0.3 7.7 ±0.2 (20.9 ± 0.6) × 10⁻³  RLuc8 6.9 ± 0.1 6.1 ± 0.1 8.9 ± 0.1 9.6 ± 0.4(198.2 ± 8.5) × 10⁻³  Since bisdeoxycoelenterazine's emission spectrumis significantly blue shifted from the other substrates, and since theluminometer's enhanced spectral sensitivity at these shorter wavelengthswas not corrected for, the absolute unit values are not accuratealthough the relative values between proteins are. Standard errors ofthe mean are reported.Mutations to Test Proposed Active Site

Based on the residues known to be critical for haloalkane dehalogenasesactivity, D120, E144, and H285 were expected to be required for Renillaluciferase activity as well. The locations of these residues in ahomology model Renilla Luciferase are shown in FIG. 4( b). To test thehypothesis that these residues comprise a portion of the enzyme's activesite, further mutations were made at these sites on the RLuc8 construct,with the results shown in Table 2. With respect to maintainingluciferase activity, mutations at these proposed active site residueswere deleterious.

Combining Mutants for a Destabilized Luciferase

In order to construct brighter yet destabilized mutants, the initialdouble mutants where compared to the single mutant C124A to identifymutations that led to increased activity without increasing serumstability (e.g. M185V) or decreased serum stability without affectingactivity (e.g. Q235A, S257G). Combining these mutations in the absenceof C124A resulted in the mutants M185V and M185V/Q235A (Table 2) thatshowed increased lability and activity in comparison to RLuc.

Testing of Mutants in Mammalian Expression

In order to determine whether the in vitro data gathered for the RLucmutants and RLuc8 would translate into the context of a mammalianreporter gene, expression vectors were constructed for RLuc,Q235A/M185V, M185V, C124A, C124A/M185V, and RLuc8 in a pcDNA 3.1backbone. These mammalian expression plasmids were then transientlytransfected into 293T cells. Measurements of light output over timefollowing transfection, as shown in FIG. 7 with respect to the RLucplasmid, demonstrated that the mutations conferred increased lightoutput following transfection in mammalian cells. A cycloheximide studywas performed to assess the enzymatic stability for the luciferasevariants in the context of the mammalian cytoplasm. As shown in FIG. 8,the relative differences in inactivation resistance, but not theabsolute differences, were consistent with the serum inactivationexperiments. Through densitometry measurements of western blotsperformed on the cell lysates, the amount of luciferase was estimatedfor the different conditions and used to calculate the specific activityvalues shown in Table 4. These values were roughly consistent with thein vitro data from bacterially expressed protein.

TABLE 4 photons/s/mole enzyme RLuc (4.2 ± 0.2) × 10²² Mutant Activity(relative to RLuc) C124A 1.6 ± 0.1 C124A/M185V 4.2 ± 0.6 M185V 2.5 ± 0.2M185V/Q235A 2.6 ± 0.2 RLuc8 4.4 ± 0.2 Estimated specific activity valuesfor Renilla luciferase and several variants expressed in mammaliancells. 48 h following transfection into 293T cells, the cells were lysedand analyzed for luciferase activity. Luciferase protein mass in thelysates was estimated via western blotting. Values were measured inquadruplicate, and standard errors of the mean are given. The estimatedactivity of RLuc is given in absolute values, with the remainingconditions given as relative to that of the RLuc condition.Conclusion

Luciferases are extraordinarily useful in a variety of experiments thatrequire reporter genes. In instances where the reporter gene isconstitutively expressed (e.g. cell trafficking studies (Beilhack, A.,Schulz, S., Baker, J., Beilhack, G. F., Wieland, C. B., Herman, E. I.,Baker, E. M., Cao, Y.-A., Contag, C. H., and Negrin, R. S. (2005) Blood206, 1113-1122)), RLuc8 should be advantageous because of its greatlyincreased light output compared to RLuc in mammalian cells.

In many reporter gene experiments, however, the investigator wishes tofollow the dynamics of gene induction and suppression. In thesecontexts, the high stability of RLuc8 might be a detriment to theexperiment, as the stability of this protein could obscure themonitoring of transient gene expression changes. The single mutant M185Vand the double mutant M185V/Q235A would be of great utility in thesecases, as both these mutants show a ˜4 fold increase in activity as wellas an increase in protein lability relative to RLuc.

An issue with the use of coelenterazine catalyzing luciferases forreporter gene assays in mammalian cells is that coelenterazine is asubstrate for MDR1 P-glycoprotein (Pgp). While the resultant transportof coelenterazine out of mammalian cells can be used to measure levelsof Pgp, in most studies this phenomenon leads to an inadvertentmodulation of signal intensity. For this reason, there has been interestin the coelenterazine analogs coelenterazine-cp and coelenterazine-n asthey are not substrates for Pgp. These analogs, however, suffer fromreduced light output when used with RLuc (see Table 2) as well as higherbackground rates of auto-chemiluminescence. The M185V mutation greatlyreduces the disadvantages of these alternative substrates. In the caseof coelenterazine-cp, the signal to background ratio when using theM185V mutation is nearly equivalent whether the native substrate or theanalog is used.

Bisdeoxycoelenterazine has been proposed as a better analog to use withbioluminescence resonance energy transfer (BRET) studies because of theincreased separation between the bioluminescence and the fluorescencespectrums. Bisdeoxycoelenterazine, however, suffers from extraordinarylow light output when used with native RLuc (Table 2) because of poorquantum yield (Table 3). Although low bioluminescence quantum efficiencydoesn't necessarily imply low light output from BRET, and increasedbioluminescence quantum efficiency may not translate into acorresponding increase in BRET output, preliminary data indicate thatbioluminescence quantum yield and BRET output are indeed related, atleast when the acceptor moiety is a variant of Aequorea GFP. Both RLuc8and the M185V mutation can be of great utility in these BRET assays, asthey confer a 20-60 fold increase in light output withbisdeoxycoelenterazine. Interestingly, although C124A alone doesn'timprove utilization of bisdeoxycoelenterazine, it appears to facilitatethe M185V mutation, as C124A/M185V has a ˜2 fold better light outputwith this substrate compared to M185V alone.

In summary, in the present example mutants of RLuc were characterizedwith respect to serum stability and light output and these results wereused to develop luciferases optimized for different purposes. An 8mutation form of RLuc (RLuc8) was created that has greatly improvedcharacteristics for use as a bioluminescent label. Compared to thenative enzyme, RLuc8 exhibited a 150 fold stability improvement inmurine serum, a 4 fold improvement in light output, and a 5 nm red shiftin the emission spectrum. The enhancement in light output arises from acombination of increases in quantum yield and improved kinetics. Adouble mutant of RLuc (M185V/Q235A) was created that has improvedperformance as a reporter gene. Compared to the native enzyme it hashalf the stability, as measured in murine serum, while incorporating aclose to 5 fold improvement in light output. These optimized Renillaluciferases represent significant improvements that will increase thesensitivity of luciferase based assays for both in vitro experiments andin vivo imaging.

Example 2 Bioluminescence Imaging of Angiogenesis in Living Subjectswith a Bifunctional Renilla Luciferase-VEGF Fusion Reporter ProteinMaterials and Methods

Cell Culture

Porcine aortic endothelial (PAE) cells with and without expression ofhuman VEGFR-2 (PAE/VEGFR-2) (kind gift of M. L. Iruela-Arispe;University of California, Los Angeles, Calif.) were cultured in Ham'sF-12 media supplemented with 10% fetal bovine serum and 1% penicillin(100 μg/ml) and streptomycin (292 μg/ml), (Invitrogen, Carlsbad,Calif.). Murine SVR angiosarcoma cells were cultured in high-glucoseDMEM supplemented with 10% fetal bovine serum and 1% penicillin (100μg/ml) and streptomycin (292 μg/ml). A375M human melanoma cells (kindgift of M. Kolodny; University of California, Los Angeles, Calif.) werecultured in high-glucose DMEM supplemented with 10% fetal bovine serumand 1% penicillin (100 μg/ml) and streptomycin (292 μg/ml). All celllines were in subconfluent (70-80%) growth prior to harvesting andcounting for tumor xenograft preparation.

Design, Expression, and Purification of Rluc8-VEGF121 (RL8-VEGF) and aVEGFR-2 Binding Mutant (RIK 83.2) and Control Rluc8 Proteins

The fusion gene Rluc8-VEGF121 encoding the protein RL8-VEGF wassuccessfully ligated using directional cloning of an amplified VEGF121PCR product into an expression vector using MfeI and SalI. Theprokaryotic expression vector (pBAD-pelB-Rluc8-EGF-His₆) has beenconstructed as previously described. Briefly, a pelB periplasmic leadersequence was placed upstream of the Rluc8 gene encoding a highly stableRenilla reniformis luciferase mutant. These eight mutations in the Rlucgene stabilize the luciferase activity of bacterially expressedrecombinant protein in serum. The coding sequence for human EGF gene wasligated downstream of the Rluc8 gene and spanned by MfeI and SalI sites.The human VEGF121 cDNA was amplified from an adenoviral genome (kindgift of R. Crystal, Cornell University) using paired primers spanningthe full length coding sequence. The 5′ primer: 5VEGFMFE(5′-ACGTCAATTGGGAATGGCAGAAGGAGGAG-3′) (SEQ ID NO: 14) contained MfeIsite. The 3′ primer: VEGFSAL3 (5′-AGGTCGACCCGCCTCGGCTTGTC-3′) (SEQ IDNO: 15) contained a SalI restriction site. After amplification, the PCRproduct was digested with MfeI and SalI for directional cloning into theMfeI and Sail-cut pBAD-pelB-Rluc8-EGF vector. The subsequent fusion geneof Rluc8-VEGF121 was separated by a two amino acid linker (Leu-Gly). Thesuccessful ligation of the Rluc8-LG-VEGF121-His₆ fusion gene (encodingthe protein probe RL8-VEGF) was confirmed by DNA sequencing. TheC-terminal hexahistidine was chosen at this location to ensurepurification of full length RL8-VEGF-His₆ fusion protein. The QuikChangeXL Mutagenesis kit (Stratagene, La Jolla, Calif.) was used to make aVEGF 121 binding mutant by converting amino acids 82-84 from Arg-Ile-Lysto Asp-Leu-Ser. The mutation confers a 50-fold decrease in affinity toVEGFR-2 compared with wild-type VEGF. The primers used for themutagenesis of the plasmid pBAD-pelB-Rluc8-VEGF121-His₆ were RIK83up.1(5′-CAA CAT CAC CAT GCA GAT TAT GGC AGC AGC ACC TCA CCA AGG CCA GCAC-3′)(SEQ ID NO: 16) and RlK83.down.1 (5′-GTG CTG GCC TTG GTG AGG TGC TGC TGCCAT AAT CTG CAT GGT GAT GTT G′-3′) (SEQ ID NO: 17) based onmodifications of primer pairs used to create binding mutants of VEGF aspreviously described. DNA sequencing confirmed successful mutagenesis.

Protein Expression

LMG 194 E. coli (Invitrogen, Carlsbad, Calif.) were transformed withpBAD-pelB-Rluc8-VEGF121-His₆ (RL8-VEGF), pBAD-pelB-Rluc8-RIK 83.2-His₆(RL8-RIK 83.2), and pBAD-pelB-Rluc8-His₆ (Rluc8) and grown to OD₆₀₀=0.7in mini-Luria-Bertani (LB)-ampicillin cultures. Larger LB-ampicillincultures were brought to a final arabinose concentration of 0.2%arabinose for induction at the prokaryotic araC promoter in the pBADvector (Invitrogen, Carlsbad, Calif.). Once induced, the cultures weregrown for 12 hours at 30° C. at 210 rpm in a rotatory incubator. Cellswere pelleted and a modified osmotic shock protocol was used to isolatethe periplasmic fractions. Periplasmic fractions were brought to 1 mMPMSF and filtered through a 0.22 μM membrane (Nalgene, Rochester, N.Y.).Periplasmic fractions were purified using Ni-NTA SuperFlow columns(QIAGEN, Chatsworth, Calif.) in 300 mM Nacl and 20 mM HEPES, pH 8.0 with20 mM imidazole in the loading and washing steps. The elution buffercontained 300 mM NaCl, 20 mM HEPES, pH 8.0 and 250 mM imidazole. Pooledfractions were subsequently concentrated in an Amicon 10,000 MWconcentrator (Millipore, Villerica, MA) and then dialyzed against 3changes of phosphate-buffered saline, pH 7.4 overnight at 4° C. in a10,000 MW Slid-A-Lyzer cassette (Pierce, Rockford, Ill.).

The luciferase activity of equal amounts of purified protein wasmeasured in a TD 20/20 luminometer (Turner Designs, Sunnyvale, Calif.)for a period of 10 seconds in the presence of 0.5 μg of coelenterazine(Nanolight Technology/Prolume Ltd., Pinetop, Ariz.).

Characterization of RL8-VEGF, RL8-RIK 83.2, and Rluc8 by SDS-PAGE andWestern Blotting and Luciferase Activity

Equal amounts (5 micrograms) of purified proteins were analyzed by gelelectrophoresis in 4-20% gradient SDS-PAGE gels under reducingconditions. The gels were stained with Coomassie Blue (Bio-Rad,Hercules, Calif.). For Western Blots, equal amounts (1 microgram) ofpurified proteins were resolved by gel electrophoresis in a 4-20%gradient SDS PAGE gel and then transferred to nitrocellulose. WesternBlot of the proteins using anti-C-terminal His-tag conjugated with HRPat 1:5000 dilution (Invitrogen, Carlsbad, Calif.) confirmed the presenceof His-tagged luciferase in all three constructs. After stripping of thenitrocellulose membrane, an anti-Renilla luciferase (RL) antibody(Chemicon, Temecula, Calif.) at 1:10,000 was used to detect the RLprotein in each of the proteins. Goat anti-mouse heavy and light chainantibody conjugated with horseradish peroxidase was used at 1:30,000 forsecondary antibody detection. The Enhanced ECL chemiluminescencedetection kit (GE Healthcare, Piscataway, N.J.) was used for exposure ofprotein bands to x-ray film.

Competition Bioluminescence Cell ELISA

PAE cells without and with human VEGFR-2 expression were platedovernight in 48 well culture dishes and incubated in serum free Ham'sF-12 media with RL8-VEGF fusion protein or RL8-RIK 83.2 binding mutantprotein for 1 hour at 37° C. in the presence of varying amounts of“cold” recombinant human VEGF 121 (PeproTech, Rocky Hill, N.J.). Cellswere washed and incubated with 0.5 μg of coelenterazine substrate andimmediately imaged in the Xenogen IVIS 100 optical cooled charge-coupleddevice (CCD) (Xenogen, Alameda, Calif.). Regions of interest (ROIs) weredrawn over the cell area and quantified in averagephotons/second/centimeter²/steradian (photons/s/cm²/sr) by using Livingcarnage Software version 2.50 (Xenogen, Alameda, Calif.).

Mouse Serum Stability Assays

Mouse serum (Calbiochem, EMD Biosciences, La Jolla, Calif.) wasaliquoted at 50 μL into mini-reaction tubes and incubated with 1 μg eachof RL8-VEGF or RL8-RIK 83.2. Time points of incubation were 0, 4, 8, 12,24, and 48 hours. PAE/VEGFR-2 cells were plated in 48 well cultureplates at 50,000 cells/well and grown overnight. After washing once inPBS, pH 7.4, cells were re-fed serum free Ham's F-12 media. 25 μLaliquots of the given incubated proteins in serum was added to each welland allowed to incubate for 30 minutes. Cells were washed 2× with PBS,pH 7.4 and then 0.5 μg of coelenterazine added per well and imaged inthe Xenogen IVIS optical cooled charge-coupled device (CCD) (Xenogen,Alameda, Calif.). Regions of interest (ROIs) were drawn over the cellarea and quantified in average photons/second/centimeter²/steradian(photons/s/cm²/sr) by using Living Image Software version 2.50 (Xenogen,Alameda, Calif.). Each condition was performed in triplicate, and errormeasurements are in S.D.

Results

Design, Expression, and Purification of Rluc8-VEGF121 (RL8-VEGF) andVEGFR-2 Binding Mutant Rluc8-RIK 83.2 (RL8-RIK 83.2) and Control Rluc8

The prokaryotic expression vector (pBAD-pelB-Rluc8-EGF-His₆) has beenconstructed as previously described. A directional cloning strategyusing MfeI and SalI sites flanking the epidermal growth factor (EGF)coding sequence was used to ligate VEGF 121 in-frame to the Rluc8 gene(FIG. 9 b). PCR oligonucleotide primers with 5′ MfeI and 3′ SalI siteswere designed for amplification of VEGF 121 from an adenoviral genomeand subsequent digestion with the restriction enzymes. The double-digestwas ligated into the pBAD-pelB-Rluc8-His₆ vector that also had beendigested with MfeI and SalI. Successful ligation was confirmed by DNAsequencing, and a dipeptide linker of Leu-Gly was the final linkerbetween the Rluc8-VEGF 121 fusion protein. LMG 194 E. coli weretransformed with the expression vector and logarithmic phaseLB-ampicillin cultures were induced with L-arabinose for induction atthe araC prokaryotic promoter for inducible expression of the RL8-VEGFprotein. The periplasmic leader sequence was used to direct translationof protein into the periplasm of the cells. Osmotic shock was used toisolate the periplasmic action of the cells and the recombinant fusionprotein was purified by metal chelate affinity chromatography.

As a control, a VEGF mutant was created using site-directed mutagenesisof three amino acids in the conserved binding portion of the VEGFprotein. The critical amino acid residues in the hairpin loop of VEGFare Arg-82, Lys-84, and His-86. Mutants were created in this bindingpocket as a control for these studies. The amino acids Arg-82, Ile-83,and Lys-84 were successfully exchanged to Asn-Leu-Ser, and the samepurification scheme was followed to isolate nearly equivalent amountsusing the osmotic shock protocol and metal chelate chromatography. As afurther control, the Rluc8 control protein was expressed and purifiedwithout the VEGF targeting domain.

Characterization of Purified Protein

The RL8-VEGF and RL8-RIK 83.2 VEGFR-2 binding mutant fusion proteinswere analyzed for retention of activity after periplasmic harvesting andnickel ion metal chelate affinity purification. Coomassie Blue stainingof equally loaded purified protein extracts showed equal intensities ofthe expected 50 kDa (VEGF 121=14 kDa, Rluc8=36 kDa) fusion proteins ineach lane labeled RL8-VEGF and RL8-RIK 83.2 (FIG. 10 z). Multipleadditional bands were identified which likely represent impurities inthe purification process. Proteolytic degradation of the protein wasexpected since it has been commonly shown that fusion proteins witheukaryotic peptide sequences can be degraded. Using an anti-C-terminalHis-tag mAb conjugated with horseradish peroxidase, single bands offusion proteins were seen, and the multiple impurities in the CoomassieBlue stained gel were not seen in the Western Blots (FIG. 10 b). Forconfirmation of correct translation of Renilla luciferase (RL) protein,the nitrocellulose membrane was stripped and re-probed using an anti-RLmAb and demonstrated recognition of RL sequences in the purifiedproteins. Non-specific background staining can be seen at highermolecular weights and likely reflects secondary antibody binding, as thepreviously probed blot with anti-C-terminal His-tag mAb does not showcorresponding contaminating bands. Rluc8 as a control was shown toresolve at the expected molecular weight of 36 kDa.

The luciferase activities were expected to be nearly equivalent betweenequal mass amounts of the RL8-VEGF and RL8-RIK 83.2 mutant. Using aluminometer the luciferase activity of purified protein (1 μg each) wasassessed and showed that the final luminescence activities of purifiedproteins were 5.50×10¹¹±2.11×10⁹ RLU/μg for RL8-VEGF and6.14×10¹¹±4.25×10¹⁰ RLU/μg for RL8-RIK 83.2 binding mutant (n=3 forboth, p<0.05).

To test for preservation of VEGFR-2 affinity of RL8-VEGF, and the lackof binding affinity of RL8-RIK 83.2, a competition bioluminescence ELISAassay was used. Porcine aortic endothelial (PAE) cells withoverexpression of human VEGFR-2 (PAE/VEGFR-2) were assayed for retentionof bioluminescence in the presence of purified proteins. Purifiedrecombinant human VEGF 121 was co-incubated in the wells of the assayplate at 0, 10, 50, and 100 ng/mL in triplicate. FIG. 10 c shows thedose-dependent inhibition of binding of RL8-VEGF with increasingconcentration of purified VEGF 121. The VEGFR-2 binding mutant RL8-RIK83.2 shows a 5-fold decrease in binding to PAE/KDR cells relative toRL8-VEGF and no dose-dependent competition from purified VEGF 121.

Serum Stability of Purified RL8-VEGF, RL8-RIK 83.2 and RLuc8:

The goal of using an injectable fusion reporter protein probe wouldrequire high serum stability in the face of factors that would decreasethe luciferase activity from the blood including proteolyticdegradation. Therefore, the serum stability of the fusion protein wasassayed to determine whether placement of the VEGF targeting portionaltered the extremely stable nature of the Rluc8 luciferase activity. 1μg of purified RL8-VEGF and Rluc8 were incubated for 0, 2, 4, 8, 12, 24,and 48 hours in mouse serum at 37° C. Aliquots of serum were assayed inthe presence of 0.5 μg of coelenterazine substrate in a luminometer intriplicate. The addition of the VEGF domain did not alter the serumstability for the Rluc8 control alone. Both RL8-VEGF and Rluc8 retained88% of their luciferase activity after 48 hours of incubation in mouseserum (FIG. 11 a).

To determine whether serum incubation would alter the VEGF affinity toVEGFR-2 over time in serum at 37° C., PAE/KDR cells were plated in 48well plates and incubated with aliquots of 50 μL of serum plus 1 μg ofeither RL8-VEGF or RIK 83.2 VEGFR-2 binding mutant at 0, 4, 8, 12, 24,and 48 hours. FIG. 11 b shows that RL8-VEGF fusion protein retained 69%of its binding and activity to VEGFR-2 on PAE cells. The VEGFR-2 bindingmutant RIK 83.2 showed only 4% binding relative to the RL8-VEGF fusionprotein binding throughout the assay from 0 to 48 hours. Rluc8 alsoshowed a very similar level of 3-5% binding throughout a separate assay(data not shown).

Discussion

The VEGFR-2 (human KDR/mouse flk-1) receptor tyrosine kinase is apotentially useful target for delivery of tracers or probes to imagenascent vascular networks in and around tumors. Since the VEGFR-2 isfound in both tumor cells and the microvasculature around these cells,the delivery of a reporter protein probe (e.g., targeting moiety) invivo makes it possible to image small micrometastases for earlydetection (see FIG. 9 a for schematic of how the VEGFR-2 targetingmoiety functions). The genes that encode for the soluble ligands, VEGF121 and VEGF 165, and for the receptor VEGFR-2 have been cloned.Attaching an enzymatic reporter protein makes it possible to identifyareas where early angiogenic signals are delivered by targeting the samepathway that cells use to recruit endothelial cells in times of hypoxiaand increased metabolic demand. The soluble form of the VEGF ligand,VEGF 121, was chosen for this purpose. An injectable 50 kDa fusionprotein was engineered for VEGFR-2 targeting and subsequentbioluminescence reporter activity in living subjects (e.g., a VEGFR-2specific targeting moiety).

Attempts at imaging angiogenesis have relied more on surrogate markersfor increased blood vessel formation such as changes in vesselpermeability, perfusion, and MRI blood pool agents. Radionuclideapproaches include PET using ¹⁸F to measure glucose metabolism and bloodpooling. Direct methods of imaging VEGFR-2 in new endothelial cellsinclude ¹²³I and ¹¹¹Indium labeled VEGF recombinant protein in tumor andpro-angiogenic gene therapy trials for ishemic heart disease,respectively. Sensitivity is the main limitation of these studies ofdirect camera imaging of angiogenic receptors. Recent reports includeusing a prokaryotically expressed VEGF targeting protein for use withSPECT detection. Optical imaging has been examined for the feasibilityof detecting gene transfer into vascular endothelial cells with greenfluorescent protein gene, but autofluorescence in background tissuelimited the signal detection²⁸. Bioluminescence reporter imaging hasbeen useful to prevent unwanted background autofluorescence and has beenutilized in reporter gene therapy studies. For this reason, exogenouslydelivered protein conjugated with fluorochrome dyes such as Cy5.5 or Cy7would have poor signal-to-noise images. Hence a bioluminescent enzymedeliverable by the fused VEGF protein as chosen and targeted to VEGFR-2on the surface of dividing endothelial cells.

The functional expression and targeting of therapeutic toxin-VEGF fusionproteins have been described using VEGF 121 fused in-frame to theDiptheria exotoxin, Shiga-like toxin, and a plant toxin, gelonin. Thepresent example demonstrates a diagnostic imaging agent withbifunctional ends with targeting and reporter activities. This targetingmoiety retained highly stable serum target binding and enzymaticactivity allowing for clearance of the agent from the blood pool overtime.

Cell cultures results using PAE/VEGFR-2 cells validated binding fromhuman VEGF 121 to human VEGFR-2. Although the human VEGF 121 codingsequence was used, good binding to mouse flk-1 receptor was expected dueto the 85% binding homology. Competitive bioluminescence ELISA againstthese cells confirmed the specific targeting of the VEGF domain toVEGFR-2. The serum stability of this protein showed 88% of retainedbinding and bioluminescence activity to 48 hours of incubation in mouseserum. In the previously described toxin-VEGF studies, therapeuticeffects were elicited regardless of the domain order in the fusionprotein. Therefore, the VEGF targeting, which resides in the internalresidues of the protein, should not be limited by the effects of proteindomains at either N-terminal or C-terminal ends. The molecular imagingof tumor xenografts have been described using a novel SPECT labelingapproach with ^(99m)Tc-VEGF.

Combined molecular imaging approaches for the earlier detection ofbreast cancer using PET and optical hand-held transducers may beimportant for earlier detection of small radiographically occult breastcancers as a complement to mammography. Mammography has achieved muchsuccess in reducing the overall deaths from breast cancer. Earlierdetection may be achieved once methods to image the events precedingcancer invasion and metastasis can be developed as an adjunct toradiographic screening.

Example 3 Development of Color Shifted Renilla Luciferase Variants

Methods

Please note that many of the methods used in this example are similar tothose from Example 1 and are not repeated here. Only those methods thathave not been previously described or have been modified are discussedbelow.

Random Mutagenesis

Random mutagenesis was accomplished using Mutazyme II (Stratagene).Following PCR, the product was purified and digested overnight in a 37°C. bacterial incubator with DpnI (to remove parental template) alongwith the appropriate restriction enzymes (NcoI/SalI) for insertion intothe plasmid backbone. After gel purification, a total of 200 ng ofmutated insert and plasmid backbone (SalI/NcoI digested pBAD) at a 2:1insert/backbone molar ratio were ligated overnight at 16° C. in a 20 μlreaction. 5 μl of the ligated product was then transformed into 50 μlTop 10 bacteria cells (Invitrogen), and spread on 8 150 mm diameterTerrific Broth/50 μg/ml ampicillin (TB/Amp) agar plates containing 0.2%L-(+)-arabinose. Following 20 h of incubation at 32° C., the plates wereairbrushed with a phosphate buffered saline (PBS) solution containing 1%0.5 mg/ml coelenterazine in propylene glycol and imaged immediatelyusing an IVIS 200 bioluminescence imaging system (Xenogen). Three 5 sacquisitions were made using a DsRed, a GFP, and an open filter.Acquired images were processed in GNU Octave using a collection ofcustom scripts. Colonies were selected both automatically with thesescripts as well as manually for brightness and/or spectral shifts.Colonies were then screened further as described below in “Small ScaleProtein Purification”.

Saturation Mutagenesis

Saturation mutagenesis at specific locations was performed by making useof Type IIs restriction enzymes and primers containing a randomizedcodon sequence. The method presented here is a modification of apreviously published protocol (Ko J K, Ma J. Am. J. Physiol. CellPhysiol. 288(6):C1273-C1278, 2005) and differs mainly in that the entireplasmid is used as the template for PCR, obviating the need for a secondligation step. Standard PCR conditions were used, with the exceptionthat the extension time was increased to 2 min/kb, 5% DMSO was includedin the reaction, template was used at 10% of usual concentrations andprimers were used at 20% of usual concentrations. restriction digestsusing BpiI (Fermentas, Hanover, Md.) and DpnI were performed overnightin a 37° C. bacterial incubator. Following gel purification, ligation,transformation, and plating was done as in the random mutagenesis case.

Small Scale Protein Expression

For random and saturation mutagenesis experiments, the clones initiallyselected from the agar plates were further screened by small scaleexpression experiments. Selected colonies were picked into 2 ml TB/Ampeach and grown to saturating conditions at 37 C (˜12 h). 2 ml TB/Ampcontaining 0.2% L-(+)-arabinose was then added to each tube and thecultures were grown an additional 12 h at 32° C. Following this, half ofeach culture was spun down and submitted to the osmotic shock protocolas described in Example 1. The periplasmic fractions were assayed forspecific activity, assayed for bioluminescence color shifts visually,and stored at 4° C. Bright and/or color shifted variants were thensubmitted for sequencing. For variants identified as having novelmutations, the periplasmic fraction was brought to 1×WB (Example 1) froma 10× stock, and further purified using nickel affinity spin columns(Ni-NTA Spin Kit, Qiagen) with 1×EB as the elution buffer. The elutionwas brought to 1% HSA, and then assayed for specific activity.Interesting color shifts were confirmed by spectrophotometry asdescribed in Example 1. As before, emission spectra were filtered asnecessary and normalized to equalize the total area under the curve.

Results

Probing of the Active Site of RLuc8

In an attempt to rationally alter the emitted wavelength of Renillaluciferase, the location and orientation of the substrate in the activepocket was conjectured. This was done by assuming the catalytic triadwas used for coordinating the oxygen, that the orientation of thesubstrate would be similar to that seen with other a/b-hydrolases, andthat the varying affinities of the different mutations in Example 1 forthe various coelenterazine analogs were due to close interactionsbetween the mutation and the altered side chain of the analog. Thisconjecture was formulated using a Swiss-Model derived RLuc8 homologystructure. The results of this exercise are shown in FIG. 12. Using thismodel of coelenterazine/coelenteramide in the active pocket as a guide,a total of 74 site specific mutations were made at the 22 residuesthought to interact with the substrate. With the exception of the I223location at which mutagenesis was saturating, the subset of possiblemutations done at each residue was selected based on what would beconsidered “safe” with respect to the tertiary fold of the enzyme. Theresults of this screen are shown in Tables 5 and 6. From this screen, atotal of 21 mutations at 10 different residue locations resulted inobservable shifts in the emission spectrum. The variants withbathochromic shift mutations presumably have active pockets that favorthe green fluorescing anion form of coelenteramide. Unsurprisingly,given that the enzymatic pocket of RLuc8 is already evolved for thereaction at hand, nearly all these mutations led to significantreductions in the light output of the luciferase.

TABLE 5 Results of site-directed mutagenesis in the active pocket ofRLuc8. Specific Actvity (relative to RLuc) Wavelength (nm) native hh cpn bdc peak mean fwhm % > 600 nm RLuc8 4.3 ± 0.2 3.0 5.8 8.8 59 486 50394 4 Active Pocket Mutations RLuc8/N53D 0.002 0.004 0.002 0.001 0.01 NDRLuc8/N53Q 0.10 0.16 0.52 0.04 0.31 475 491 92 3 RLuc8/N53S 0.001 0.0020.003 0.005 0.03 ND RLuc8/W121F 0.05 0.02 0.02 0.03 0.15 478 496 94 3RLuc8/W121H 0.003 0.002 0.004 0.01 0.02 ND RLuc8/W121Y 0.003 0.007 0.010.01 0.01 ND RLuc8/V146I 1.1 1.1 0.60 0.50 21 484 502 95 4 RLuc8/V146M1.0 0.66 0.51 0.47 0.43 481 498 94 3 RLuc8/V146W 0.000 0.000 0.000 0.0000.000 ND RLuc8/I150F 0.51 0.56 0.50 1.0 5.3 485 504 95 4 RLuc8/I150H0.53 0.25 0.19 2.6 8.1 494 514 98 6 RLuc8/I150M 2.9 1.8 3.1 2.2 24 488508 95 5 RLuc8/I150W 0.94 0.65 0.62 1.3 8.2 485 503 94 4 RLuc8/I150Y0.02 0.01 0.02 0.29 0.15 487 506 97 4 RLuc8/W153F 4.9 3.1 4.9 7.9 104484 502 95 4 RLuc8/W153Y 1.2 0.75 1.1 2.1 15 485 503 96 4 RLuc8/W156F3.9 2.7 7.2 12 81 486 504 93 4 RLuc8/W156H 0.46 0.48 0.53 2.3 1.2 490510 96 5 RLuc8/W156Y 3.0 2.6 5.2 9.0 91 483 501 94 4 RLuc8/I159F 0.600.43 0.56 1.7 1.4 491 510 101 5 RLuc8/I159H 0.04 0.04 0.02 0.11 0.53 506526 108 10 RLuc8/I159W 0.12 0.13 0.08 0.44 0.28 490 508 104 6RLuc8/I159Y 0.003 0.002 0.01 0.05 1.1 513 536 113 13 RLuc8/I163F 0.570.80 0.39 0.61 7.6 483 502 95 4 RLuc8/I163H 0.16 0.21 0.12 0.19 6.1 499519 102 7 RLuc8/I163W 0.16 0.26 0.15 0.26 2.1 498 517 103 7 RLuc8/I163Y0.13 0.16 0.10 0.14 1.2 502 521 103 8 RLuc8/I166F 1.3 1.2 1.1 1.8 11 483501 96 4 RLuc8/I166H 0.04 0.08 0.03 0.05 0.52 483 502 100 4 RLuc8/I166L4.4 2.4 5.3 9.5 55 486 506 92 4 RLuc8/I166W 0.004 0.01 0.003 0.01 0.20 498^(†) 508 110 7 RLuc8/I166Y 0.23 0.35 0.16 0.34 2.5 493 508 99 5RLuc8/F180I 0.63 0.65 0.62 0.70 8.7 486 504 101 5 RLuc8/F180W 4.0 2.43.3 4.6 45 485 502 93 4 RLuc8/F180Y 3.0 2.2 2.6 3.4 52 484 499 105 4RLuc8/F181W 0.07 0.05 0.05 0.13 4.8 479 494 95 3 RLuc8/F181Y 0.07 0.110.03 0.06 1.2 497 515 103 6 RLuc8/K189E 4.4 2.6 3.8 6.7 61 484 501 95 4RLuc8/K189H 3.6 2.0 1.8 6.1 44 485 502 94 4 RLuc8/K189I 1.1 1.0 4.4 1.919 484 500 96 4 RLuc8/K189R 0.70 0.86 0.58 0.45 1.1 484 502 93 4RLuc8/P220H 0.003 0.003 0.003 0.01 0.05 ND RLuc8/P224H 0.08 0.03 0.070.004 0.29 484 500 95 4 RLuc8/Y240F 5.6 2.0 4.4 5.3 48 484 502 92 4RLuc8/F261W 0.20 0.38 0.38 0.02 0.76 504 524 98 8 RLuc8/F261Y 0.07 0.930.53 0.01 16 487 506 97 4 RLuc8/F261W/F262W 0.000 0.000 0.00 0.002 0.003512 531 115 11 RLuc8/F262W 0.60 0.20 0.23 0.07 0.02 500 521 99 7RLuc8/F262Y 0.01 0.01 0.01 0.001 0.04 511 532 104 10 RLuc8/F286W 0.080.11 0.07 0.04 0.24 481 499 92 3 RLuc8/F286Y 0.07 0.08 0.23 0.05 0.24482 501 93 4 The data for RLuc8 is repeated from Table 2 for the purposeof comparison. Y240 is not believed to be in the active pocket, but isproximal to it. Substrate abbreviations are as previous. Spectra weremeasured using coelenterazine. Specific activities are relative to thatof RLuc 1 and were not corrected for the luminometer's wavelengthdependent sensitivity. ^(†)RLuc8/I166W showed a shoulder peak at 415 nmthat was 28% of the height of the main peak at 498 nm. FWHM—full widthat half maximum. ND—not determined.

TABLE 6 Results of saturation mutagenesis on RLuc8 at the putativeactive pocket residue of I223, along with some double mutants. SpecificActivity (relative to RLuc) Wavelength (nm) native h cp n bdc peak meanfwhm % > 600 nm RLuc8 4.3 ± 0.2 3.0 5.8 8.8 59 486 503 94 4 I223Mutations RLuc8/I223A 0.68 0.37 0.94 0.51 2.0 ND RLuc8/I223C 3.0 1.7 6.23.7 12 503 524 103 9 RLuc8/I223D 0.01 0.01 0.01 0.06 0.10 503 524 106 9RLuc8/I223E 0.01 0.01 0.01 0.11 0.21 497 517 104 7 RLuc8/I223F 2.7 2.11.8 2.5 10 486 505 92 4 RLuc8/I223G 0.14 0.07 0.12 0.33 1.3 498 518 1057 RLuc8/I223H 0.07 0.05 0.09 0.43 1.9 508 527 105 9 RLuc8/I223K 0.0020.002 0.001 0.003 0.26 491 509 97 5 RLuc8/I223L 1.3 1.8 1.2 1.4 16 483502 95 4 RLuc8/I223M 0.19 0.37 0.25 0.64 14 501 521 98 7 RLuc8/I223N0.30 0.31 0.33 0.48 1.7 505 527 102 9 RLuc8/I223P 0.01 0.01 0.01 0.030.13 486 505 96 5 RLuc8/I223Q 0.06 0.06 0.06 0.31 2.3 505 527 102 9RLuc8/I223R 0.003 0.002 0.002 0.01 0.24 505 528 108 10 RLuc8/I223S 0.610.45 0.49 0.71 1.7 499 517 104 7 RLuc8/1223T 0.43 0.36 0.33 0.48 0.54499 517 102 7 RLuc8/I223V 2.5 1.9 2.8 3.0 31 490 509 97 5 RLuc8/I223W0.003 0.004 0.01 0.02 0.01 484 508 104 7 RLuc8/I223Y 0.02 0.02 0.02 0.040.07 486 605 97 4 Double Mutants RLuc8/I223C/F261W 0.12 0.12 0.43 0.010.03 511 529 104 8 RLuc8/I223C/F262W 0.07 0.02 0.09 0.01 0.01 511 529100 8 RLuc8/I223H/F261W 0.002 0.003 0.005 0.01 0.02 ND RLuc8/I223H/F262W0.001 0.001 0.001 0.01 0.01 ND RLuc8/I223M/F261W 0.02 0.01 0.01 0.010.05 ND RLuc8/I223M/F262W 0.002 0.001 0.001 0.01 0.001 NDELuc8/I223Q/F261W 0.003 0.005 0.003 0.01 0.02 ND The data for RLuc8 isrepeated from Table 2 for the purpose of comparison. Substrateabbreviations are as previous. Spectra were measured usingcoelenterazine. Specific activities are relative to that of RLuc andwere not corrected for the luminometer's wavelength dependentsensitivity. FWHM—full width at half maximum. ND—not determined.Random Mutagenesis on RLuc8Round 1—Random Mutagenesis on RLuc8/F261W, RLuc8/F262W

The original purpose of the random mutagenesis study was to take some ofthe red-shifted mutations identified in the active pocket site directedmutagenesis study and improve their catalytic abilities. The RLuc8/F261Wand RLuc8/F262W variants were picked as starting points, as they bothgave rise to appreciable bathochromic shifts while not overlycompromising the light output of the luciferase. Random mutagenesis wasperformed on these templates, and screened in bacteria for bothincreases in light output as well as emission color shifts. The resultsof this study are given in Table 6. Interestingly, several mutationlocations were over represented. Of these mutations, those at residuesE155 and G269 lead to increases in light output, and those at D162 leadto further bathochromic shifts in the emission spectra.

TABLE 7 Results of random mutagenesis on RLuc8/F261W and RLuc8/F262W.Specific Wavelength (nm) Activity peak mean fwhm % > 600 nm F261WMutants RLuc8/F261W 0.20 505 524 98 8 RLuc8/R11P/F261W/V267I 0.25 501522 99 7 RLuc8/A22P/D162N/F261W 0.10 526 547 97 13RLuc8/V63I/L94F/F261W/F278I 0.36 501 522 98 7 RLuc8/R93L/D162E/F261W0.05 535 551 112 17 RLuc8/L94F/F261W 0.15 501 521 97 7RLuc8/K113R/E155K/F261W 0.54 503 523 98 7 RLuc8/A123S/F261W 0.48 504 52398 7 RLuc8/M143T/F261W 0.26 503 523 98 7 RLuc8/D162N/F261W/S188N 0.05525 544 97 13 RLuc8/A164T/D248E/F261W/K297N 0.12 502 521 98 7RLuc8/F261W/N264S 0.27 503 523 99 7 RLuc8/F261W/K271R 0.14 505 526 99 8F262W Mutants RLuc8/F262W 0.60 500 521 99 7 RLuc8/Q26K/E155K/F262W 0.75500 521 99 7 RLuc8/P65H/A130T/F262W 0.12 501 522 99 8RLuc8/F105V/E151K/D162E/F262W 0.07 535 551 119 18 RLuc8/A123S/F262W 0.50499 519 98 7 RLuc8/E155G/E183D/F262W 0.89 501 522 98 7RLuc8/E155K/E169D/F262W 0.60 501 521 98 7 RLuc8/K167M/K173N/F262W 0.54498 519 98 7 RLuc8/V234I/F262W/G269R 0.86 501 523 99 8 RLuc8/F262W/G269E0.57 500 520 98 7 RLuc8/F262W/G269R 1.3 502 523 100 8 RLuc8/F262W/M295V0.47 499 520 98 7 Mutation locations that showed up multiple times aredesignated by bold text. The data for RLuc8/F261W and RLuc8/F262W isrepeated from Table 6 for the purpose of comparison. Coelenterazine wasused for measuring the spectra and specific activity. Specificactivities are relative to that of RLuc (Table 2) and were not correctedfor the luminometer's wavelength dependent sensitivity. FWHM—full widthat half maximum.Round 2—Saturation Mutagenesis at D162/I163

As the A123S mutation showed some potential for increasing the lightoutput of RLuc8/F261W, it was incorporated into RLuc8, RLuc8/F261W, andRLuc8/F262W by site specific mutation. Although this mutation issomewhat detrimental for RLuc8 and RLuc8/F262W, it was retained with theidea that a later round of mutagenesis would be done at the F261 site.These three A123S containing templates, along with RLuc8, were used forsaturation mutagenesis at the D162 residue identified in the previousrandom mutagenesis screen. As the D162 residue borders the active pocketresidue I163, this residue was incorporated into the saturationmutagenesis screen as well. Results of saturation mutagenesis atD162/I163 performed on the templates RLuc8, RLuc8/A123S,RLuc8/A123S/F261W, and RLuc8/A123S/F262W are given in Table 8. Quitesurprisingly, a single point mutation (D162E) could lead to asignificant red-shift of the emission spectra of the luciferase withouta severe compromise in the luciferase's ability to output light. Alsointeresting, is that several of the selected mutants had significantside peaks around 410 nm. This side peak is presumptively emanating fromthe neutral species of coelenteramide. For RLuc8/A123S/D162L/I163V, itgives the variant a whitish purple color when the bioluminescence isvisualized.

TABLE 8 Results from saturation mutagenesis at the D162/I163 residues ofRLuc, RLuc8/A123S, RLuc8/A123S/F261W, and RLuc8/A123S/F262W. SpecificWavelength (nm) Shoulder/ Activity peak mean fwhm shoulder Peak Ratio% > 600 nm Clones RLuc8 Mutants RLuc8 4.3 486 503 94 4 RLuc8/D162E 1.4522 537 108 12 1 RLuc8/D162E/I163M 1.2 519 530 108 10 1RLuc8/D162E/I163T 0.08 539 547 125 19 1 RLuc8/D162N 2.1 510 526 96 4080.05 8 2 RLuc8/D162N/I163V 1.6 516 531 103 408 0.08 10 6RLuc8/D162P/I163L 0.28 525 515 103 406 0.50 10 1 RLuc8/D162S/I163V 4.7485 504 92 4 1 RLuc8/A123S Mutants RLuc8/A123S 2.8 484 502 92 4RLuc8/A123S/D162C/I163V 0.95 520 539 94 11 1 RLuc8/A123S/D162E 1.5 522536 107 12 2 RLuc8/A123S/D162E/I163L 2.4 523 538 102 12 2RLuc8/A123S/D162L/I163V 0.29 532 515 124 409 0.75 13 1 RLuc8/A123S/D162N2.0 509 526 96 407 0.05 8 1 RLuc8/A123S/D162N/I163L 2.4 507 523 93 4040.07 7 2 RLuc8/A123S/D162N/I163S 0.19 523 535 110 407 0.18 13 2RLuc8/A123S/D162T/I163C 0.10 527 514 119 409 0.69 12 1 RLuc8/A123S/F261WMutants RLuc8/A123S/F261W 0.48 504 523 98 7 RLuc8/A123S/D162T/F261W 0.23526 547 102 14 1 RLuc8/A123S/D162E/F261W 0.21 533 547 116 16 1RLuc8/A123S/D162E/I163L/F261W 0.12 538 553 107 17RLuc8/A123S/D162N/I163M/F261W 0.29 520 539 95 11 3RLuc8/A123S/D162N/I163V/F261W 0.21 531 551 102 16 3 RLuc8/A123S/F262WMutants RLuc8/A123S/F262W 0.50 499 519 98 7RLuc8/A123S/D162E/I163V/F262W 0.06 541 558 113 21 1RLuc8/A123S/D162N/F262W 0.23 527 544 100 13 1 If the spectrum had ashoulder peak, it is noted above along with the ratio of the height ofthe shoulder peak to the main peak. Clones indicates how many coloniescoded for the same protein sequences (but not necessarily the samenucleotide sequence), and is an indicator for how well the search spacewas covered. The data for RLuc, RLuc8/A123S/F261W, and RLuc8/A123S/F262Wis repeated from previous tables for the purpose of comparison.Coelenterazine was used for measuring the spectra and specific activity.Specific activities are relative to that of RLuc, and were not correctedfor the luminometer's wavelength dependent sensitivity. FWHM—full widthat half maximum.Round 3—Saturation Mutagenesis at F261/F262

Using RLuc8/A123S and RLuc8/A123S/D162E/I163L as templates, saturationmutagenesis was done at the F261/F262 residues in an attempt to find thebest color shift residues at this location. Out of ˜15,000 coloniesscreened the mutagenesis with RLuc8/A123S as the template, onlyparental, Luc8/A123S/F261W, and RLuc8/A123S/F262W clones were selectedby the screen. Out of ˜9000 colonies screened from the mutagenesisperformed using RLuc8/A123S/D162E/I163L as the template, the onlynon-parental clone selected by the screening process wasRLuc8/A123S/D162E/I163L/F261W. The results of this screen would indicatethat no further improvements in either light output or color shift weremade at the F261/F262 position.

Round 4—Saturation Mutagenesis at I223/P224

As saturation mutagenesis at I223 yielded several bathochromic shiftmutations, saturation mutagenesis was performed on the I223/P224location, as well as on the 5 residues P220/R221/E222/I223/P224. Thetemplates used in this screen were RLuc8 and RLuc8/A123S/D162E/I163L.For each of these 4 conditions, ˜4000 colonies were screened for lightoutput and/or color shifts. All the clones selected from thismutagenesis were the parental sequence, and were either parentaltemplate that had escaped the DpnI digestion, or templates containingsilent mutations. No further optimization was seen in this region of theprotein.

Round 5—Saturation Mutagenesis at V185/L186

With respect to increases in light output, the M185V mutation was themost interesting one that arose from the consensus sequence drivenmutagenesis of Example 1. For this reason, saturation mutagenesis atV185/L186 and V185/L186/P187/S188/K189 was performed on the templatesRLuc8 and RLuc8/A123S/D162E/I163L. The results of this screen are shownin Table 9. Interestingly, the V185L mutation coupled toA123S/D162E/I163L could lead to a further ˜8 nm bathochromic shift inthe emission spectrum, but when V185L was present alone in the RLuc8background it led to no observable shift in the emission.

TABLE 9 Results from saturation mutagenesis at V185/L186, as well asrandom mutagenesis over V185/L186/P187/S188/K189. Specific Wavelength(nm) Activity peak mean fwhm % > 600 nm RLuc8 Mutants RLuc8 4.3 ± 0.2486 503 94 4 RLuc8/V185L 3.3 485 504 95 4 RLuc8/V185Q 4.5 482 500 93 3RLuc8/V185K/L186M/P187A/S188A/K189L 0.85 480 497 102 4RLuc8/A123S/D162E/I163L Mutants RLuc8/A123S/D162E/I163L 2.4 523 538 10212 RLuc8/A123S/D162E/I163L/V185L 2.1 532 545 106 15RLuc8/A123S/D162E/I163L/V185L/L186F 0.72 530 541 110 14RLuc8/A123S/D162E/I163L/V185A/P187V/S188K/K189M 0.31 510 525 113 10 Thetemplates used for mutagenesis were RLuc8 and RLuc8/A123S/D162E/I163L,and for the purposes of comparison the data for these variants isrepeated from previous tables where Coelenterazine was used formeasuring the spectra and specific activity. Specific activities arerelative to that of RLuc, and were not corrected for the luminometer'swavelength dependent sensitivity. FWHM—full width at half maximum.Round 6—Saturation Mutagenesis at D154/E155

Some of the more promising candidates from the previous rounds ofmutagenesis were selected for saturation mutagenesis at the E155position. E155 had been identified in the initial random mutagenesisscreen as a residue that could be mutated to increase the light outputfrom the RLuc8/F261W and RLuc8/F262W constructs, and it was hoped thatmutagenesis at this location would lead to improvements inRLuc8/A123S/D162E/I163L/V185L, RLuc8/A123S/D162E/I163L/F261W, andRLuc8/A123S/D162E/I163V/F262W. The neighboring D154 position wasincluded in this saturation mutagenesis screen as well. The results ofthis screen, shown in Table 10, demonstrated that significantimprovements of all three parental constructs could be achieved bymutagenesis at these two positions.

TABLE 10 Results from saturation mutagenesis at the D154/E155 residues.Specific Wavelength (nm) Activity Peak Mean fwhm % > 600 nmRLuc8/A123S/D162E/I163L/V185L Mutants RLuc8/A123S/D162E/I163L/V185L 2.1532 545 106 15 RLuc8/A123S/D154M/E155G/D162E/I163L/V185L 3.5 535 550 10417 RLuc8/A123S/D154R/E155T/D162E/I163L/V185L 2.9 531 546 104 15RLuc8/A123S/E155G/D162E/I163L/V185L 3.4 532 545 104 15RLuc8/A123S/D162E/I163L/F26lW Mutants RLuc8/A123S/D162E/I163L/F261W 0.12538 553 107 17 RLuc8/A123S/D154K/E155N/D162E/I163L/F261W 0.97 545 560106 21 RLuc8/A123S/D154R/E155G/D162E/I163L/F261W 0.39 537 554 106 18RLuc8/A123S/E155G/D162E/I163L/F261W 0.66 537 554 107 17RLuc8/A123S/E155K/D162E/I163L/F26lW 0.46 541 556 107 18RLuc8/A123S/D162E/I163V/F262W Mutants RLuc8/A123S/D162E/I163V/F262W 0.06541 558 113 21 RLuc8/A123S/D154A/E155G/D162E/I163V/F262W 0.60 547 564111 23 RLuc8/A123S/D154T/E155G/D162E/I163V/F262W 0.54 544 560 112 21RLuc8/A123S/D154V/E155G/D162E/I163V/F262W 0.87 543 560 112 21RLuc8/A123S/E155G/D162E/I163V/F262W 0.80 543 560 111 21 The templatesused for mutagenesis were RLuc8/A123S/D162E/I163L/V185L,RLuc8/A123S/D162E/I163L/F261W, and RLuc8/A123S/D162E/I163V/F262W. Thedata for these parental constructs are repeated from previous tables forthe purpose of comparison. Coelenterazine was used for measuring thespectra and specific activity. Specific activities are relative to thatof RLuc. Note that the spectral sensitivity of the luminometer'sdetector penalizes the red-shifted variants, and this was not correctedfor here. FWHM—full width at half maximum.Round 7—Saturation Mutagenesis at G269/A270

In an attempt to further improve the green emitting luciferase variants,the results of the previous screen at the D154/E155 positions wereapplied to an additional saturation mutagenesis screen at the G269/A270positions. The G269 residue was identified in the initial randommutagenesis screen as a position at which mutations could lead tosignificant improvements in the light output of RLuc8/F262W. With thisin mind, saturation mutagenesis of G269 and the neighboring residue A270was performed on the parental constructsRLuc8/A123S/E155G/D162E/I163/V185L,RLuc8/A123S/D154K/E155N/-D162E/I163L/F261W, andRLuc8/A123S/D154V/E155G/D162E/I163V/F262W. between ˜3000-6000 colonieswere screened for each condition, but no improved variants (with respectto light output or red-shift) were identified in the selection process.

Round 8—Random Mutagenesis on RLuc8/A123S/D154V/E155G/D162E/-I163V/F262W

In an attempt to identify locations that may yield further red-shifts inthe bioluminescence emission spectrum, theRLuc8/A123S/D154V/E155G/D162E/-I163V/F262W construct was subjected torandom mutagenesis. In a small screen of ˜15,000 colonies, no furtherimprovements in either light output or emission spectrum red-shifts wereobserved.

Discussion

The data in this chapter shows that a green emitting coelenterazineusing luciferase is indeed possible, presumably due to favoring thepyrazine anion of coelenteramide in the enzymatic pocket. Further more,this shift in spectrum can come with little loss in the ability of theluciferase to emit light. Bioluminescence emission spectra for two ofthese variants are shown in FIG. 13 in comparison to emission spectrafrom the click beetle luciferases.

An interesting question to ask, is how much of an effect on in vivoimaging capabilities could be expected from the ˜25-65 nm emissionshifts that the luciferase variants present here. The expected benefitof these bathochromic (red) shift variants is complicated by the factthat these shifts are moving the peak emission squarely into a localmaximum around 550 nm in the hemoglobin absorption curve. To answerthese questions, rough calculations of light attenuation were made usingrat liver absorption values. Rat liver was chosen as a model organ tostudy because the absorption values are available in the range ofwavelengths that are of interest here.

A quantitative comparison is given in Table 11, where predictions aremade as to the relative gain in light output versus RLuc for the variousluciferase variants at 0.1 and 0.5 cm depth of liver tissue. Again,these results underscore the advantageousness of having a red-shiftedRenilla luciferase for small animal imaging applications. They alsopoint out that the benefits of red-shifting the emission spectrumoutweigh any penalties from the local hemoglobin absorption peak at 550nm.

TABLE 11 Effects of tissue depth on the relative light output of severalRenilla luciferase variants. Specific Corrected Wavelength % TransmittedEffective Output Activity Activity mean (nm) 0.1 cm 0.5 cm 0.1 cm 0.5 cmRLuc 1.0 1.0 497 2.8 0.025 1.0 1.0 RLuc8 4.3 4.3 503 3.1 0.029 4.7 5.0RLuc8/A123S/D162L/I163V 0.29 0.35 515 5.7 0.17 0.71 2.4RLuc8/A123S/D162N/I163L 2.4 3.1 523 4.2 0.065 4.7 8.1RLuc8/A123S/D162E/I163L 2.4 3.6 538 5.8 0.13 7.4 19RLuc8/A123S/D162E/I163L/V185L 2.1 3.4 545 6.9 0.18 8.4 25RLuc8/A123S/D154M/E155G/D162E/I163L/V185L 3.5 6.0 550 7.4 0.20 16 48RLuc8/A123S/D154K/E155N/D162E/I163L/F261W 0.97 1.9 560 8.7 0.26 5.9 20RLuc8/A123S/D154A/E155G/D162E/I163V/F262W 0.60 1.2 564 9.7 0.31 4.2 15Note that the spectral sensitivity of the luminometer's detectorpenalizes the red-shifted variants; the “Corrected Activity” takes thisinto account using compensation factors. “% Transmitted” is the percentof photons that are transmitted through the given depth of rat livertissue, as calculated based on the spectra data and rat livertransmittance data. “Effective Output” is the corrected specificactivity of the enzyme multiplied by the percent of photons transmittedfor the given depth. The effective output values as well as the specificactivity values have been normalized to those of RLuc.

It is evident from the above results and discussion that the presentdisclosure provides an important new class of luciferase proteins thatgreatly expands the utility of these molecules in a variety of differentapplications. As such, the subject disclosure represents a significantcontribution to the art.

Although the foregoing disclosure has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it is readily apparent to those of ordinary skill in theart in light of the teachings of this disclosure that certain changesand modifications may be made thereto without departing from the spiritor scope of the appended claims.

SEQ ID NO. 1 (Renilla reniformis wild-type luciferase polynucleotidesequence); SEQ ID NO. 2 (Renilla reniformis wild-type luciferasepolypeptide sequence); SEQ ID NO: 3 (RLuc/A55T); SEQ ID NO: 4(RLuc/S130A); SEQ ID NO: 5 (RLuc/K136R); SEQ ID NO: 6 (RLuc/A143M); SEQID NO: 7 (RLuc/M253L); SEQ ID NO: 8 (RLuc/S287L); SEQ ID NO: 9(RLuc/Q235A); SEQ ID NO: 10 (RLuc/S257G); SEQ ID NO. 11 (Rluc/M185V);SEQ ID No: 12 (Rluc8 polynucleotide sequence); SEQ ID NO. 13 (Rluc8protein sequence); SEQ ID NO: 14; SEQ ID NO: 15; SEQ ID NO: 16; SEQ IDNO: 17; SEQ ID NO: 18 (RLuc8/I159H); SEQ ID NO: 19: (RLuc8/I163Y); SEQID NO: 20: (RLuc8/F181Y); SEQ ID NO: 21: (RLuc8/I223C); SEQ ID NO: 22:(RLuc8/F261W); SEQ ID NO: 23: (RLuc8/F262W); SEQ ID NO: 24:(RLuc8/A123S/D162E/I163L); SEQ ID NO: 23: (RLuc8/A123S/D162N/I163L); SEQID NO: 26: (RLuc8/A123S/D162E/I163L/V185L); SEQ ID NO: 27:(RLuc8/A123S/D154M/E155G/D162E/I163L/V185L); SEQ ID NO: 28:(RLuc8/A123S/D154K/E155N/D162E/I163L/F261W); SEQ ID NO: 29:(RLuc8/A123S/D154A/E155G/D162E/I163V/F262W); SEQ ID NO: 30:(RLuc8/A123S/D154V/E155G/D162E/I163V/F262W); SEQ ID NO: 31 (RLuc8/N53Q);SEQ ID NO: 32 (RLuc8/A54P); SEQ ID NO: 33 (RLuc8/D120N; SEQ ID NO: 34(RLuc8/W121F); SEQ ID NO: 35 (RLuc8/V146I); SEQ ID NO: 36 (RLuc81V146M);SEQ ID NO: 37 (RLuc8/F181W); SEQ ID NO: 38 (RLuc8/F286Y).

1. An isolated polynucleotide encoding a mutant Cnidarian luciferase,wherein the mutant luciferase has the sequence of SEQ ID NO:27.
 2. Thepolynucleotide of claim 1, wherein the polynucleotide encodes a fusionprotein comprising the mutant Cnidarian luciferase and at least onefusion partner.
 3. The polynucleotide of claim 2, wherein the at leastone fusion partner comprises an epitope tag.
 4. The polynucleotide ofclaim 2, wherein the at least one fusion partner comprises a targetingmoiety.
 5. The polynucleotide of claim 4, wherein the targeting moietyis selected from the group consisting of: an antibody, a receptor, aligand, and binding fragments or mimetics thereof.
 6. The polynucleotideof claim 5, wherein the targeting moiety is a ligand that specificallybinds to VEGF receptor
 2. 7. The polynucleotide of claim 6, wherein thetargeting moiety is VEGF
 121. 8. A construct comprising: a vector and apolynucleotide according to claim
 1. 9. An expression cassettecomprising: a polynucleotide according to claim
 1. 10. A cell, or theprogeny thereof, comprising an expression cassette according to claim 9as part of an extrachromosomal element or integrated into the genome ofa host cell as a result of introduction of the expression cassette intothe host cell.
 11. A method of producing a luciferase, the methodcomprising: growing a cell according to claim 10, whereby the protein isexpressed; and isolating the protein substantially free of otherproteins.
 12. A kit comprising: a polynucleotide according to claim 1.13. The kit of claim 12, wherein the kit further comprises a substratefor the luciferase.
 14. The kit of claim 13, wherein the substrate is acoelenterazine.